How dead is my battery?

soylentgreen · May 2013

My RV has two Trojan T145s. I opened them up today to check the water levels, and.... they were a bit low. I couldn't see the water level but it was below the top of the plates. I don't know the age of the these (no "manufactured in..." sticker) but I've had this van since 2008 so they are at least 5 years old, and I know during the 5 years I've had them, I've not treated them well: Let them sit at 50%+ or more discharge for weeks, and never had a decent charger. So they should be basically toast.

The funny thing is, they still seem to work - they hold a charge and seem in many ways to operate as I'd expect.

My experience & rule of thumb with automotive starting batteries is "if it's 5 years old, replace it", but that's usually with no-name brands. Our gracious hosts have an excellent price (if I can deal with shipping).

Any advice?

Is there a way to diagnose their health?

westbranch · May 2013

Re: How dead is my battery?

what does your Hydrometer tell you as to SG?

Cariboocoot · May 2013

Re: How dead is my battery?

Exposed plates is very bad for batteries.
Fill them to just above the plates with distilled water and fully charge them. Add water if it bubbles off below plate level while charging. Check SG after charging, add distilled water to proper level. Charge again. Equalize to see if SG can be brought up.

Then go buy new ones. Five+ years old, exposed plates, known mistreatment ... even if they come out "good" they aren't going to last.

BB. · May 2013

Re: How dead is my battery?

What happens if they die?

The old risk/reward tradeoff... If they die and you just go get a new set from down the road--No big deal to keep using this.

If they die and cause you to abandon vacation (or an on-site job)--Then the risk is probably not worth it. These batteries have lasted you pretty well (most people kill their first set or two of off grid batteries long before they die of old age).

-Bill

niel · May 2013

Re: How dead is my battery?

as coot said, they will not last very long so complete failure is inevitable. battery manufacturers may vary on their definitions of being dead, but for mine it states 80% of capacity. that does leave some power to be had even though it is technically dead to the manufacturer. they do soon go to complete failure after reaching the point manufacturers specify though. bill's point is they probably don't need replaced today, but it depends on availability and how dependable you want it to be. it would be a gamble as to how long they would deliver the useable power to you.

soylentgreen · May 2013

Re: How dead is my battery?

Specific Gravity: I've never done that test, but sounds like one I should know how to do.

Cost/Benefit: good questions. If I can the T145s at a good price, I'll probably just replace them, as those are the largest ones I can fit. If not, then I might drop down to the Costco golf cart batteries which are available locally at about 1/2 the price - but are also a little smaller.

niel · May 2013

Re: How dead is my battery?

do go with a hydrometer and keep a log book of battery facts and check on them at least once a month for water levels, sg, and cleaning/inspecting.

soylentgreen · May 2013

Re: How dead is my battery?

So I just ran a quick & dirty test.

Fully charged batteries with a decent charger (does bulk/equalize/float). Watered the batteries (when I discovered they were low). Re-charged.

Then I ran them for 24 hours with a RV fridge which is known to draw about 15W (about 30AH/day). Turned off the fridge, waited 3 hours, then checked the voltage: 12.50V

Googling "battery SOC chart" gives a lot of opinions. Several sources claim "12.50 V = 90% SOC"

If true, then this means 10% SOC = 30AH, so 100% SOC = 300AH.

The Trojan Chart: http://lib.store.yahoo.net/lib/wind-sun/Trojan-specifications-guide.pdf indicates that these T145s have, at a 100H rate, 287AH.

An optimist might say "Hey, these batteries are just like new!"

But I suspect it's not so simple: do old,tired,abused batteries sometimes look fine on light-load testing, but then fail on testing with higher DOD and/or higher amp testing?

Cariboocoot · May 2013

Re: How dead is my battery?

soylentgreen wrote: »

But I suspect it's not so simple: do old,tired,abused batteries sometimes look fine on light-load testing, but then fail on testing with higher DOD and/or higher amp testing?

Yes. Got it in one.
Like the difference between a 'D' cell and a triple 'A'; Voltage may read the same but the capacity isn't there.
So when you put a heavy load on that the batteries should be able to supply, the Voltage drops drastically.
Or is you try to supply the expected 'X' Amp hours @ rate you run out long before the 20 hours is up.

T145 should be 260 Amp hours, quite a substantial battery. A refrigerator is not a consistent load; it cycles on and off. If it drew 15 Watts steady that would be 1.25 Amps, fairly insubstantial to the T145's.

Try applying something that draw about 20 Amps and see what happens to the Voltage when you do.

soylentgreen · May 2013

Re: How dead is my battery?

Cariboocoot wrote: »

Yes. Got it in one.
Try applying something that draw about 20 Amps and see what happens to the Voltage when you do.

These batteries are connected to a 2000W (4000W surge) MSW inverter. I think I can test anything from 0 to TOOMANY watts. If I were to do one test, what's the sweet spot?

Side question: I've read a number of times that running batteries "hot" (high voltage charging, to equalize & bubble them up a lot) is good for them.
Is high wattage DISCHARGE also good for them? Does hitting them with a 100A load magically "unfrangle" the "foobarium" and make them happy?

Cariboocoot · May 2013

Re: How dead is my battery?

Hitting a 260 Amp hour battery with a 100 Amp load will flatten it in no time at all. High current discharges are not good for them, but cycling them down below 75% SOC occasionally is good.

Too high charge current or Voltage is not good for them either. High Voltage will bubble off the water faster. High current will create more internal heat.

Approximately 300 Watt load on your inverter should draw around 26 Amps @ 12 Volts (inverter included) and would be a 10% discharge rate for those batteries. Check what happens to the Voltage when you have that much load on.

The only reconditioning you might try is to run a load on it until you've pulled it down to 12 Volts under load. Then recharge, making sure you have a long enough Absorb time. Then let them rest with no load for a day and check the Voltage. See if it's still 12.7 after that.

soylentgreen · May 2013

Re: How dead is my battery?

I dont have a 300w load handy , but the van has a 500w 120vac water heater, which I figure is about 600W total including inverter losses.
With a fully charged battery I ran this heater for 0.5 hours. While running the voltage dropped to 12.19. After sitting for an hour the voltage was back up to 12.62.

BB. · May 2013

Re: How dead is my battery?

It sounds promising... How many Watt*Hours/Amp*Hours do you need to get from your bank (assuming it is good)... Run your 600 Watt AC load (at 85% inverter eff and 12 volt battery) gives about 58 Amp load) for that amount of time (2 hours ~ 116 AH used) or until the battery bank hits ~11.5 volts (stop discharging there to prevent battery damage).

If the bank maintains your loads, and the batteries don't get too hot--They should be fine.

If you can get 3x 100 watt bulbs for a 300 watt load (or whatever your average "real load" would be), and get a better figure of merit for your true needs.

-Bill

How dead is my battery?

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