Winter Battery Woes.....

Busby573 · October 2010

I figured people here would have a better knowledge of batteries and battery maintenance, so here is my situation.

I live in Northern Idaho, and run my house of a small Off-Grid .66 KW solar system. The system was set up by my Dad and myself, (He does electrical, so it was easy enough to figure out).

It consists of:

- Three 220 Watt solar panels
- Twelve 12V 105AH AGM batteries
- 48V smaller Xantrex Inverter,(probably a mid to later 2000"s model)
- Outback charge controller
- 8 KW stationary propane generator
- Other parts that are obviously needed for the system

The system works fantastic, besides the fact that during the Winter when we get very limited sun, the batteries preform very poorly and drop voltage when no load is on them.

During late Spring to Late Fall, we have absolutely no consumption problems. We are very conservative with our electricity usage, using on average about 2.5KW per day. The generator never goes on and we have an abundance of electricity.

During the Winter however because of our location and the fact that we have a small mountain that the sun tends to go behind, most of the electricity being put into the batteries comes from the backup generator which is started via an automated GSM whenever the inverter thinks the batteries need charging.

Now I know for a fact batteries love being charge by solar, and hate being charged by generators,(Slow charge vs Forced charge). I also understand that charging batteries via a generator too much can damage their life. These batteries are all less then 2 years old however, and during the Summer when they are happy they hold maybe 3KW of electricity between being fully charged at 50V and being depleted at 46.8V,(This is what I'm reading on the charge controller). During the Winter it's only about 2KW, and the biggest problem is that they drop serious amounts of voltage all day long with no load on them. For example if I let the generator fully charge them, then not use any electricity today, by tomorrow they will be down in the low 47V range.

Batteries are expensive and I just fail to see why even when they are charged properly, 12 105AH batteries only hold 3KW of electricity, the equivalence of what the average American burns through in a matter of hours daily.

Right now our propane generator runs for a little over an hour a day, seperated into several different short run periods per day, (I think the inverter is trying to compensate to the fact that they batteries are not holding their charge).

Our yearly propane bill really isn't that expensive, but being an efficiency freak it bothers me that electricity is just disappearing into thin air.

Anyone think this sounds strange, or is this just the reality of dealing with trying to store energy?

Kamala · October 2010

Re: Winter Battery Woes.....

Busby573 wrote: »

... - Other parts that are obviously needed for the system ...

Tell us about the battery charger between the generator and the battery bank.

Also, do you have a temperature sensor on your batteries? And are they in a warm or cold place? Your generator ought to able to charge your batteries as well, if not better, than your PV panels. Consequently, I suspect a problem with the battery charger or temperature compensation/environment.

K

Cariboocoot · October 2010

Re: Winter Battery Woes.....

Short form: 12 105 Amp hour batteries configured for a 48 Volt system = 3 parallel strings of four batteries each totaling 315 Amp hours @ 48 Volts nominal.
Minimum charge current required: 15.75 Amps @ 56.8 Volts (the battery manufacturer should provide specifics).
Panels: 3 * 220 Watts = 660 @ 80% efficiency (best case) = 528 "usable" Watts. Divide by 56.8 Volts charging = 9 Amps. Doubling the array size would be good.

So there's your first problem: not enough panel.
If this has been going on for some time your second problem is toasted batteries from chronic under-charging. You're right: you should have at least 3.7 kW available. If the gen starts automatically when/as needed the under-paneling shouldn't be an issue. 50 Volts for an "at rest" reading is okay, but if that's what the Absorb Voltage is set at it's way under.

Like Kamala said; what about the charger? There's different grades and you really should be using a "3 stage" unit meant for deep cycle batteries.

And there is always the issue of wiring the bank. It's so easy to choke off current with too small wire or, more commonly, not get even distribution among parallel banks.

You might want to invest in a battery monitor, since there's no way to look inside an AGM and see what state it's in. http://store.solar-electric.com/metersmonitors.html

Kamala · October 2010

Re: Winter Battery Woes.....

'Coot,

Thanks for doing the routine calcs. I sidestepped them because the OP'er claimed excellent performance in the summer months. Such performance may, or may not, be there but assuming it is, the most suspect inadequacies are related to the charger or temperature.

Kamala

Cariboocoot · October 2010

Re: Winter Battery Woes.....

Kamala wrote: »

'Coot,

Thanks for doing the routine calcs. I sidestepped them because the OP'er claimed excellent performance in the summer months. Such performance may, or may not, be there but assuming it is, the most suspect inadequacies are related to the charger or temperature.

Kamala

Yes indeed!

But you can often get away with more power use in Summer because you're using while the sun shines; not relying on battery capacity to keep you going 'til the next charge cycle. The lights aren't on so long either.

Kamala · October 2010

Re: Winter Battery Woes.....

O Woe! Woe upon woe to come! So vast a sea of possibilities to which I am blind.

Still, I find this statement curious:

Busby573 wrote: »

... Now I know for a fact batteries love being charge by solar, and hate being charged by generators,(Slow charge vs Forced charge). I also understand that charging batteries via a generator too much can damage their life. ...

Batteries don't "care" where the energy comes from as long as it is the correct balance of volts and amperes at the right time. This correct balance is dynamic and changes as the battery approaches full charge.

Could this be a 12V generator? That certainly would be damaging!

K

Cariboocoot · October 2010

Re: Winter Battery Woes.....

Actually the OP isn't too far off right. Batteries do prefer the charge profile of solar as opposed to a battery charger's output. The panels start off with low current, increase as the sun gets 'round the panels, bring the Voltage up, level off, back down on the current, then settle into a Float Voltage. A charger hits the batteries with maximum current from the start, brings up the Voltage while tapering off the current, and finally settle down to a "trickle" current which is not necessarily Voltage dependent. The exact "charge profile" of either will vary with the charge controller/battery charger.

The difference seems to be the level of current at the start. Beginning with full current heats the battery faster, and a hot battery is not as receptive to charging. In short, it may prevent a proper/long enough Absorb cycle.

Caveat: no official studies have been done on this as far as I know. So far it's still in the realm of anecdotal evidence. But a lot of people have observed this phenomenon independently and come to the same conclusion: batteries 'prefer' solar.

Kamala · October 2010

Re: Winter Battery Woes.....

Arrgh! Love ya man BUT...

Let's assume that all energy sources are properly sized. Or, even better, let's determine the charging needs. With proper controllers or chargers, the same charge would be applied to the batteries.

It might be that the OP'er does not have this set up but for the sake of argument.... ?

Kamala · October 2010

Re: Winter Battery Woes.....

Cariboocoot wrote: »

... Batteries do prefer the charge profile of solar as opposed to a battery charger's output. The panels start off with low current, increase as the sun gets 'round the panels, bring the Voltage up, level off, back down on the current, then settle into a Float Voltage. A charger hits the batteries with maximum current from the start, brings up the Voltage while tapering off the current, and finally settle down to a "trickle" current which is not necessarily Voltage dependent. The exact "charge profile" of either will vary with the charge controller/battery charger. ...

True enough. But can't battery chargers be built to emulate "solar charging profiles?" And if they can, why aren't they.

Cariboocoot · October 2010

Re: Winter Battery Woes.....

Kamala wrote: »

Arrgh! Love ya man BUT...

Let's assume that all energy sources are properly sized. Or, even better, let's determine the charging needs. With proper controllers or chargers, the same charge would be applied to the batteries.

It might be that the OP'er does not have this set up but for the sake of argument.... ?

Relax!

I'm just trying to explain this weird charge phenomenon that many people have noticed.

Solar panels: charge begins at about 1 Amp, and as more sun falls on the panel the output can ramp up to the maximum available. This happens over hours. Meanwhile, the slower rate charge has "replaced" some Amp hours and brought the Voltage up. Net result: less time spent at the peak charge Voltage (hopefully enough to re-mix the electrolyte in FLA's).

Typical battery charger: charge begins at full current, as Voltage comes up current drops off. Thus more time is spent charging at higher current rates.

Batteries seem to Absorb better with the solar charge pattern.

Here's some fun trivia for you: if you've got a really dead car battery and your automatic car battery charge puts out zero Amps when you out it on, turn on the headlights. The charger's output will go up in response to the added draw. Shut the headlights off after a minute; the charger output will stay above zero and 'force' current into the defunct battery. Then when you get the thing started, go buy a new battery.

Busby573 · October 2010

Re: Winter Battery Woes.....

Thanks for the reply's guys.

Incoming electricity doesn't seem to be a problem, as during the summer they are always full considering we get 3-4KW per sunny day(We have long days in summer, short days in winter due to northern exposure) and during the winter the generator produces way more electricity then the batteries can absorb within an hour period. According to the inverter, the Input is set at 20 Amps maximum, so while the generator puts out 8KW it's only accepting less then half that. If I wanted to save propane, I could definitely try to get a 4KW Generator when this one dies, but it's hard to find stationary home backup generators that you can wire to a GSM under 8KW.

I'm curious when you say 50V at resting period is ok, but it could go higher. I'll admit in the middle of summer they get charged up to 52V at resting, but during the Winter they just don't seem to want accept anything past 50V,(or at least the inverter isn't allowing it).

Cold could be an issue, I wasn't sure how much it could affect the batteries. My house is probably not at an optimal battery temperature seeing as how I'm a resource hoarder I don't burn firewood 24/7 during the winter. On average the house is probably 58 Degrees inside. Right now the batteries are just open, no cover boxes or anything. Do you guys think I should possibly make an insulated box to cover them with? Would you have to vent the box with AGMs? I'm pretty sure I have a battery temperature sensor, not sure if it's hooked up though, I need to check.

The battery cables seem pretty beefy, we actually made some homemade ones when we added more batteries to the system, which is easy enough to do,(Wire, shrink wraps, connectors).

I'm gonna get you guys a picture of the setup so maybe it will make better sense.

Busby573 · October 2010

Re: Winter Battery Woes.....

As far as system settings, I'm pretty sure they are all at what basicly the inverter manual/charge controller manual tell you to put as defaults regarding to specific system sizes/voltages/batteries.

Right now I'm kinda thinking the issue is spawning from the air temperature and maybe some of the system settings.

stephendv · October 2010

Re: Winter Battery Woes.....

I am guessing here, but I think 1 hour charge time on the generator is too short. It sounds like the batteries aren't spending enough time in Absorb.
To summarise the data you've given:
- 315Ah battery at 48V
- Generator runtime when charging = 1 hour
- Maximum charging current = 20A

So everyday you're putting back 20Ah into the bank, that's 960Wh; which doesn't match your 2.5kwh/day usage. It looks like batteries aren't being properly charged by the generator. You could try a few things:
- Increase the absorb time programmed in the inverter/charger.
- Since you have AGM batteries, you could charge them faster than lead acid's. 20A is only 6% of 315Ah which is really the minimum you can charge at, you could go as high as 20% - so to be safe, you could change the charge current to 47A (15%).

And wait for someone with more experience with batteries to confirm what I've suggested above!

dwh · October 2010

Re: Winter Battery Woes.....

Yea, a few short runs totaling an hour a day @ 20a isn't going to cut it.

20a charge x 48v (nominal) would be .96kw per hour as stevendv says, so to recharge 2.5kw at that rate would take at least 2.6 hours.

Still curious what charger the generator is powering.

There might be two temp sensors - one for the solar charge controller, and one for whatever AC powered charger is running from the generator. That is, IF the AC charger has a connection for a temp sensor. If it does, then it should have one, if it doesn't - oh well...ya run whatcha brung.

It seems to me that fully charged resting voltage for a 48v system should be up around 54v (13.5 x 4) or 54.8 (13.7 x 4) and charging voltage should be 56.4 (14.1 x 4) or 57.6 (14.4 x 4).

It sounds like maybe the inverter is shutting down the generator before the batteries are fully charged. Maybe the voltage set point for generator shutdown is too low.

And yea, for that much battery 30a-40a at 48v should be in the sweet spot (10%-13%) for charge rate.

Busby573 · October 2010

Re: Winter Battery Woes.....

Now that you have mentioned that... that makes total sense. It's only letting in in reality 20 Amps within an hour period, which certainly isn't 2.5KW.

Can anyone else confirm that it's not going to kill anything to increase the Input amp charge? Sounds like increasing it to 40Ah would help solve some of my problems. I also agree that the batteries are likely not being floated or anything, they are just bulk charging and then back to resting.

Also, sounds like I could increase the full-resting battery voltage higher, the inverter may not be actually charging them full.

Still curious what charger the generator is powering.

As far as I understand, the generator sends AC Power to the inverter, which is then converted to DC and sent through the black Outback Box into the batteries,(the black box is the charge controller). The generator is 220, so it's actually sending that power through one leg, we have the other leg hooked to various outlets in the house for doing laundry etc... while the generator is running,(allowing you to charge the batteries and get straight power at the same time). I think the Inverter does most of the battery monitoring however, seeing as how most settings are changed on the inverter instead of the battery controller.

My dad was the one who essentially programmed everything, so he knows the settings better then I do, though I have a general understanding.

stephendv · October 2010

Re: Winter Battery Woes.....

The inverter is actually an inverter and a charger in one device (inverter/charger). The generator is connected to that directly and it's this charger that is charging the batteries. The outback FM is purely for use by the PV panels.

With regards to increasing the charging current, that alone is not going to solve your issues, if you just change the 20A to 40A, then all it will do is reach the voltage set point faster. I.e. it will run for 30 minutes instead of an hour.

The most important thing to do is to program the charger to complete the charge cycle, this is most likely done through setting voltage set points on the inverter/charger. Once this is correct, you'll be charging the batteries all the way up using the generator; then you can optimise the time required by changing the max current from 20 to 40 for example.

BB. · October 2010

Re: Winter Battery Woes.....

Yes, you can charge at ~40-50 amp rate of charge into your 315Ah battery at 48V battery bank. And from a genset point of view, that would be actually better (more fuel efficient, less overall runtime).

Roughly, a good rate of charge from your genset would be around 50%+ of the generator's rated capacity:

8,000 watts * 1/0.50 * 1/0.80 inverter eff * 1/58 volts charging = 55 amps

Once you have the battery 80-90% charge--you can shut down the genset and let the solar array take the batteries to near 100% charged.

Regarding AGM's, you will want to monitor their temperature during charging to insure that they do not overheat (should not be a problem for your bank, but you always want to be careful when changing major settings).

Regarding the "resting" charge voltage... Roughly, 13.6 volts * 4 = 56.4 volts would the "Float" voltage for your bank (long term charging voltage to maintain full charge). True resting voltage (several hours of no charging/no loads) would be around 12.7v*4=50.8volts...

Of course, all the above are based on a battery ~77 degrees F.

Always refer back to the Manufacturer's specification for battery charge settings/timing.

If you do not have a Battery Monitor (see Marc's post), you might want to consider one... Because you cannot measure specific gravity in sealed/AGM batteries--you are left with few ways of checking the state of charge of the battery bank other than "resting voltage".

And, with AGMs, they are very sensitive to overcharging (too much current, batteries will overheat and vent gas/electrolyte). Normally, you will not want to charge above ~14.4v*4=58.6volts -- And once the battery is "full", drop the charging voltage to float voltage.

-Bill

Cariboocoot · October 2010

Re: Winter Battery Woes.....

The Voltages should be pushed up. A "48 Volt" system should be absorbing around 57 Volts, not 50.
The time in Absorb should be increased; at least 2 hours or shut down when the current drops below ~ 3 Amps.

If you've only been charging to 50 Volts for a long time (a year of daily cycles) chances are the batteries are ruined - as in sulphated resulting in less than full capacity, which would exhibit the symptoms you describe (unable to hold charge).

(And before someone starts the argument, yes AGM's do sulphate. It just doesn't happen as quickly as with FLA's. It's the same chemical action inside. No, I will not engage in a long and pointless argument over the issue. It doesn't matter to me: I'm not buying your batteries.

)

bryanl · October 2010

Re: Winter Battery Woes.....

re: "12 105AH batteries only hold 3KW" -- always use the proper units! (KW is power and AH at a specified voltage is energy)

12 times 105 means 1260 AH at 12v or 15 KwH. Optimum cost efficiency is for nominal discharge to about 50%. That means about 7 KwH of energy should be available for normal use from the battery bank.

De-rate that for temperature and also for use if you pull large currents. Cycle to cycle variance can also add up to 10% or more variance in available energy.

Of course, that is only for fully charged, happy, batteries.

What batteries like from a charge first and foremost is sufficient time to get fully charged. This means 8 to 12 hours or more of carefully applied current.

Generally, charging with lower currents for a longer time keep a battery happier. You need a couple of times the self discharge rate as a minimum to get any decent charging but you don't want a max rate more than C/5 or so to avoid overheating and other problems.

But the problem most genset charging has is that of trying to push too much too fast and not allowing the chemistry to get fully settled. The problem with most solar charging is too little current for too short a time not getting a full and complete charge. Careful design can ameliorate these issues.

mike95490 · October 2010

Re: Winter Battery Woes.....

My only obversation, is that charge at 50V is not enough, bulk should be 54, absorb 56-58V, and the occasional "EQ" up near 60 V for brief periods, per battery mfg spec. (what ever the mfg spec is)

In cold weather, battery capacity begins to drop

But I think you have been undercharging for a long time.

westbranch · October 2010

Re: Winter Battery Woes.....

Some specifics on the model and settings of the CC and the Inver-charger would also help this discussion a lot.

Do you also have some better pics of the wiring ? One can not see if there are equal wire lengths from the one posted.

Also do a resting check (3 hours min after charge stops) ( and post it ) of each 12v battery and each 48 v bank.

Look in the inver-charger manual and let us know the 'idle draw' rate (watts) of the I-C as this may be part of the depletion you mentioned in the original post.

cheers
Eric

Kamala · October 2010

Re: Winter Battery Woes.....

Busby573,

I think that the advice given by all will set you on the path to correct your problems. But there are still some pertinent questions.

1. How long has this system been operating?
2. What is the model # of your Xantrex charger/inverter?
3. What temp sensors do you have connected?
4. Is the battery bank connected with equal length cables and wired according to the methods described at http://www.smartgauge.co.uk/batt_con.html?

Don't schedule a funeral for your batteries quite yet. They may have significant life remaining.

Also, I noticed in the photos that the battery terminal connections are secured with wing nuts. These connections should be equally torqued at the same force. If the battery manufacturer cannot supply a standard, choose something reasonably arbitrary and make sure each connection is torqued at the same force. This is not a trivial matter. Nor is equal cable length.

Good luck!

K

dwh · October 2010

Re: Winter Battery Woes.....

mike90045 wrote: »

and the occasional "EQ" up near 60 V for brief periods, per battery mfg spec. (what ever the mfg spec is)

Careful with AGMs though - some do specify the occasional EQ, but many say don't EQ. As Mike says, you have to check the specs for your batteries.

Busby573 · October 2010

Re: Winter Battery Woes.....

First of all, the wire connectors are all the same length except for 2 longer connectors that were needed because of the limited space where the batteries are stored. There is only room for 6 batteries on each level, so obviously if there are 3 strings of 4 they cannot all be the same length.

As far as wing-nut torque tightness, my dad over-tightens EVERYTHING. So they are all likely stupidly tight, and around a similar torque I would guess considering when you tighten something there is a limit to how tight it will go.

There is a battery temperature sensor hooked up to one of the batteries, on the inverter it says battery temperature is 15C' = 59F. Someone said optimal AGM temperature is 77F, so that's an 18 degree difference. The temperature didn't change after being charged. I don't think I have to worry about them overheating, that's for sure.

The Inverter/Charger is a Xantrex 2.5KVA 48VDC 120VAC 60HZ
Model: SWPLUS2548, Circa 2005 manufacturing date.

I tried increasing the charging Amps, but it won't go any higher then 20. I'm thinking possibly the inverter is so small it simply won't do anything higher then 20.

Last winter we ended up with a Dead-Soldier, basically one of the batteries was not holding a charge, and it was concurrently dropping the whole voltage of the system even though the rest were holding. I'm gonna check the individual voltage of each battery later today to see if that's a problem.

I think I figured out why the inverter is only running the generator for short periods of time. This morning it only went on for 20 minutes, obviously not enough time to even get near a full charge. However on the voltage indicator, they were bulk charged until 56V, floated for a short period of time at about 54V, and then the generator went off. According to those numbers, the inverter thinks they are technically full, and is just doing what it is supposed to.

This could mean a couple of things I'm thinking. The first would be that they are actually semi-full and it's just one or a couple weak-link batteries that are dragging down the voltage.

Another would be that the battery system as a whole is somewhat shot, and is charging very quickly and losing it's charge very quickly. Basically the battery life has been killed.

Busby573 · October 2010

Re: Winter Battery Woes.....

I just took an individual battery reading and it looks like my first theory is correct thankfully and not thankfully.

12.36V
12.4V
12.28
12.36
12.38
12.10
12.10
12.08
12.11
11.11
10.3
10.2

So it looks like some weak links are slowly losing their voltage and dragging down the overall system voltage while the majority of the batteries are fine. Do you think these batteries could have been harmed because of the 2 long connectors as opposed to the rest of the connectors being the same length?

dwh · October 2010

Re: Winter Battery Woes.....

Busby573 wrote: »

Do you think these batteries could have been harmed because of the 2 long connectors as opposed to the rest of the connectors being the same length?

Yes, certainly. Here's the straight dope on imbalanced battery connections and exactly what happens because of it:

http://www.smartgauge.co.uk/batt_con.html

The bottom line:

"The result is that the bottom battery is worked harder, discharged harder, charged harder. It fails earlier. The batteries are not being treated equally.

Now in all fairness, many people say "but the difference is negligible, the resistances are so small, so the effect will also be small".

The problem is that in very low resistance circuits (as we have here) huge differences in current can be produced by tiny variations in battery voltage."

Busby573 · October 2010

Re: Winter Battery Woes.....

That is very interesting.... especially considering the peculiar fact that of the 3 bad batteries, one exists in each bank. According to the above explanation however, the bottom battery in each Bank is the one that is going to get fried first, however that's not the case here. Here the fried batteries are random within each Bank.

Also, we don't have our batteries wired like that,(I think it's called paralleling)
Here's a better picture of the wiring. See the blue tape? Those are the bad batteries.

Not sure of the term for the way they are wired, but it's basically: Negative - Positive - Negative - Positive, and then each bank is attached to each-other by negative-negative or Positive-Positive. Here is a crude diagram.

Right now I am considering just taking out the bad batteries and having 2 banks of optimal batteries. Something is wrong though, because the exact same thing happened last year when we only had 2 banks of batteries. Except since we only had 2 banks, only 2 batteries went bad, I'm assuming one from each bank like the current case is.

In reality, with this setup there is only 1 Connector that is different then the rest,(The one on the far left connecting the left bank together). So I fail to understand why because of that 1 Connector, batteries would fail in separate banks who would all have the same Connector length.

Also consider that the battery that did fail on the left bank was not directly connected to the long Connector. Something is going on, I just don't know what.

BB. · October 2010

Re: Winter Battery Woes.....

When you get rid of the bad batteries... Check (and log) each battery's voltage under "heavy" charging and discharging... If everything is well--then each battery should be within 0.1 volts of every other battery (probably within 0.01 volts is closer to what we really want).

The father apart the voltage is from "average"--the more problem you have.

When you find a battery above/below the others--you need to figure out why. Is the current in the string being shared properly--or is one parallel string carrying a bunch more current during the load/charging.

Check for voltage drop across each cable and connection (a DMM with 200 mVolt scale is great). Again, you are not looking for zero voltage drop--but equal voltage drop across all similar cables/connections.

If you see a high voltage drop--that could mean one of two things... Either it went "high resistance" (bad, dirty, corroded connection) or you are seeing low resistance with high current (this string has good connectivity, but it is taking all the current while the other string is barely participating).

If you can justify it--A DC Clamp Current Meter can be very helpful (one like this is $100 or so).

Otherwise, I just use a common length of cable in each string (say 1 foot) and measure the voltage drop on for each string... The cable with the most voltage drop is carrying the most current--And the cable with the least voltage drop is carrying a small amount of current (poor-man's shunt resistor).

Once you get a good idea of the current flow though your bank, and the voltage at each battery--You will have a better idea if they problems are yours (poor wiring) or the vendor (poor batteries).

-Bill

mike95490 · October 2010

Re: Winter Battery Woes.....

If you wired like your sketch, expect problems. I think the sketch is wrong, or just too fuzzy.

dwh · October 2010

Re: Winter Battery Woes.....

Busby573 wrote: »

Also, we don't have our batteries wired like that,(I think it's called paralleling)

The way yours are wired is called series-parallel. You wire however many in series to get a "string" and then parallel the strings.

[EDIT: In your case, 4 x 12v batteries in series to get a 48v string, and then 3 x 48v strings in parallel to create a 48v bank.]

A series string by itself doesn't have the imbalance issue, because it's just a single straight though path, but when you parallel the series strings, then you can have the issue - where the imbalance will work one string harder. But with series-parallel you also have the issue of keeping the strings the same as each other.

Imagine the SmartGauge example where each battery is a string of 4.

Say you have one string with 1' of cable between each battery, and another with 2' of cable between each battery and then you parallel them (in a balanced fashion as per SmartGauge). The string with the shorter wires between batteries will have the least resistance and do the most work.

So, each string has to be the same as the other strings (total end-to-end resistance of the string), and then the strings also have to be paralleled in a balanced fashion.

Which is all well and good, but you're right - it doesn't explain the failure of a battery in the middle of a string.

One thing I note from what you've said is that you've replaced a few batteries. Around here the general opinion seems to be that having batteries of different ages in the same bank is a "bad thing".

I'll have to leave it to someone else to elaborate on that, as I'm sure I don't understand the details well enough to explain it.

Kamala · October 2010

Re: Winter Battery Woes.....

Here is my interpretation of the wiring diagram. The colors indicate a discrete series string. The red x marks the bad batteries.

Winter Battery Woes.....

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