# Can new Golf cart Barreries be bad?

Registered Users Posts: 3
Howdy Guys,

Sorry to bother, but I am getting nowhere fast. I have been trying to get a 6.5 amp fridge to run on my solar sysytem using 4 6-volt golf cart batteries. With over 840 amh available and my fridge using 6.5 A per hour, shouldn't I get over 125 hours of use without a charge?

I have 600 watts of solar coming in with a 500 watt turbine to keep them charged, but I am not getting anymore than 10 hours of life before I hit 50% battery alarm. I even bought 4 new batteries and am still having the same issue.... any thoughts out there, am I missing something? Do I need to buy an MPPT charge controller?

I live in Puerto rico, and I want to be set before the next hurricane season, so any advise is welcome.

Welcome to the forum Pete.

I think you are mixing series/parallel connection of batteries and how the Volts+AH capacity works...

Batteries connected in series, add voltage. Batteries (strings of batteries) connected in parallel add AH capacity.

If you have 4 x 6 volt @ 210 AH "Golf Cart" batteries connected to form a 12 volt battery bank:
• 2x batteries in series = 2*6V =12 volts
• 2x parallel strings of batteries = 2 * 210 AH = 420 AH capacity
• 2s x 2p = 12 volts @ 420 AH battery bank
You presently have 4x GC batteries... No matter how you arrange them (1s x 4p, 2s x 2p, 4s x 1p for 6v/12v/24v battery bank), the hold teh same amount of stored energy.
• 4 batteries * 6 volts * 210 AH = 5,040 Watt*Hours of capacity
And typically you want to use a maximum of 25% of that energy per day for full time off grid (for various reasons).

Now--the refrigerator. Is this 6.5 Amps as 12 volts? Is this a 12 VDC fridge, or a 120 VAC @ 6.5 amp fridge? Have you measured the current vs just looking at name plate?

If this is a 12 volt @ 6.5 Amp fridge:
• 12 volts * 6.5 Amps = 78 Watts
• 5,040 WH * 0.25 daily discharge = 1,260 WH per day
• 1,260 WH per day / 24 hours = 52.5 Watts average supported load (overnight, over 24 hours for cloudy day)
• 52.5 WH per day / 12 volts = 4.375 Amps average supported load
If your fridge is 6.5 amps @ 12 VDC and 50% duty cycle--That is an OK match with your battery bank.

That is a "reasonable number" for a 12 volt fridge... If this was a full size 120 VAC Energy Star typical refrigerator, they draw around 100-120 Watts @ 50% duty cycle (on 30 minutes/off 30 minutes as an example). And there are defrost heater(s) that draw (very roughly) 600 Watts for X to XX minutes per day to melt the ice on the evaporator.

Just to give you an idea of how the numbers could work:
• 420 AH / 6.5 amps =  64.5 hours from 100% to "dead"
• Very roughly, your refrigerator runs at 50% duty cycle once everything is cool/stable (i.e., warm food in fridge, needs to cool, making ice, compressor runs longer, etc.). So a fridge at 50% duty cycle is using 6.5 Amps * 0.50 = 3.25 Amps "on average"
However, if this is a full size 120 VAC fridge with an AC inverter:
• 6.5 Amps * 120 VAC = 720 Watts (that would be a large fridge in a defrost cycle.
• Typically around 120 Watts @ 50% duty cycle for compressor
• 120 Watts / 12 VDC = 10 Amps @ 12 volt battery bank
• 420 AH * 0.50 capacity = 210 AH
• 210 AH / 10 amp average load = 21 hours to 50% discharge
Note mixing Amps at 120 VAC and 12 VDC gets very confusing very quickly. Roughly, the AC current is 10x larger on a 12 volt battery bank. Power = Voltage * Current ... 1/10th the voltage then 10x current for same power (watts).

Before I go much further--Can you confirm the battery bank and refrigerator (12 VDC?) numbers and configuration?

The problem with refrigerators, they use quite a bit of energy (Watt*Hours per day)... And they are what take a small/cheap off grid power system and make it a relatively expensive medium size off grid power system.

If you need a small DC RV type fridge (medicine, a little bit of fresh food), a little bit of LED lighting, cell phone charging, you can get by with a smaller system... However, if you want a full size fridge, water pumping, LED TV, Laptop computer, cell phone charging, etc... That is going to take more \$\$\$.

Anyway... Don't spend any more money just yet. 1) make sure your battery bank (flooded cell deep cycle lead acid batteries?) are getting well charged (leaving FLA batteries discharged below ~75% capacity will cause them to sulfate in days/weeks and ruin them). And 2) look at your loads, measure/estimate there usage, and are you looking at 5 days of emergency power, or being off grid for months(?) while things are slowly being put back together.

Don't worry too much about the numbers/math above... It can be confusing jumping into the middle with insufficient information. Telling us about your loads and needs--Then we can logically go through your system design and get it working for you.

-Bill
Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
• Solar Expert Posts: 6,006 ✭✭✭✭✭
edited March 2021 #3
Bill addressed most of the things I would have...

For quick work figuring out capacities, sometimes it works out easiest to convert every thing to watts. A 210 amp 6 volt golf cart batteries stores about 210 amps(per hour discharged over 20 hours) x 6 volts = 1260 watthours, 4 would store about 5000 watthours.

PeteinPR said:
I have 600 watts of solar coming in with a 500 watt turbine to keep them charged, but I am not getting anymore than 10 hours of life before I hit 50% battery alarm. I even bought 4 new batteries and am still having the same issue.... any thoughts out there, am I missing something? Do I need to buy an MPPT charge controller?
What are you charging with now?
If you need a MPPT type charge controller will depend on the VMP of the solar panels. panels with a vmp of 17.5-20 will work with a PWM charge controller, Higher VMP's (Voltage under load) require MPPT type charge controllers to get reasonable use from their higher VMP output.
Often 'small wind' come with their own charge controllers, Does yours?

...and yes, you can get a bad battery! Without any recharging, you might look at the date of manufacture as well, might be an old battery!
Home system 4000 watt (Evergreen) array standing, with 2 Midnite Classic Lites,  Midnite E-panel, Magnum MS4024, Prosine 1800(now backup) and Exeltech 1100(former backup...lol), 660 ah 24v Forklift battery(now 10 years old). Off grid for 20 years (if I include 8 months on a bicycle).
- Assorted other systems, pieces and to many panels in the closet to not do more projects.
• Registered Users Posts: 3
Morning Bill,

Thank you so much for your time and level of detail in your explaination above. The information you provide has left me more confused (this just shows you how much I do not understand) but I will breakdown your questions, the best I can.

Here is the drawing of how my batteries are wired:

I have 4 Sam's Club 6 volt GC batteries that are flooded cell deep cycle lead acid batteries. The fridge that I want to operate is full size 120 VAC Energy Star typical refrigerator, with the name plate showing 6.5 Amps.

My system uses 600 watts of solar and 1 wind turbine with a max of 500 watts. I have a simple

# Digital All In One Charge Controller with LED Meter for 3 Phase and DC System

I have this wired to a

# Renogy 2000W 12V Pure Sine Wave Battery Converter, ETL Listed with Built-in 5V/2.1A USB port,and AC Hardwire Port Solar Power Inverter

So that is the best I can describe my system..... can you help me?

Thanks Bill

Pete,

There is usually an Energy Star tag that comes with the refrigerator (or can look online at the EnergyStar website).

Because you have a full size 120 VAC refrigerator--While pretty efficient, they just use both a lot of energy (Watt*Hours) per day, they also take a lot of current to start the compressor and run the defrost heater(s). I will do the "minimum" design--Just run a fridge, but you are getting to the point where you are looking at a larger system to run your whole home.

You did not say if this was an "emergency" system for a week, vs full time off grid--But if you are looking at weeks to months off grid, you really need a full size "off grid" system (not cheap).

And as Photowhit says--I will do this in Watts (a rate--like miles per hour) and Watt*Hours (an amount, like miles driven in a day).Amps and Amp*Hours are a "partial unit"--You need to know what voltage is is measured at... P=V*I:
• P=V*I= 12 volts * 6.5 Amps = 78 Watts
• P=V*I= 120 volts * 6.5 Amps = 780 Watts or 10x as much power at 120 VAC vs 12 VDC
You will need to decide how much "safety factor" you need for your system. The solar+battery system has to be relatively large because of the high starting surge of the fridge compressor & defrost heaters. Like a large truck to get the load moving, even though not a lot of power is needed to go 25 MPH down the country road. And a 12 volt battery bank is a bit on the "small side" to supply the starting surge--But it can work.

First, you need a 12 Volt TSW/PSW (true/pure sine) AC inverter in the 1,200 to 1,800 Watt range. Next sizing the battery bank. 2 "rules"... One is to supply the starting surge, the second to supply the daily energy usage--Typically 2 days of storage and 50% maximum discharge (longer battery life). First surge (note, using lots of design rules that work well--I will not go into the details "why" for now--We can talk about later if you are interested)
• 1,200 Watt inverter * 100 AH * 1/250 Watt inverter (at 12 volts) = 480 AH @ 12 volt minimum battery bank
• 1,500 WH per day EnergyStar typical fridge energy usage * 1/0.85 AC inverter eff * 2 days storage * 1/0.50 max discharge (longer battery life) = 588 AH @ 12 volt battery bank
Your 4x GC battery bank (6 volt @ 210 AH) is  on the small side (2s x 2p) or 12 volts @ 420 AH. I will do the design based on 6 GC Batteries--It will be more reliable for you. You can get 2x more batteries and wire them with the first 4 batteries--Or you can get a full set of 6. The first 4x batteries could have been damaged (I don't know). At this point, you might just keep the first 4x batteries and get the rest (solar panels, etc.) configured and test the system... Once up and running, adding/replacing the batteries then (or before hurricane season) might still be a good idea.

Next, calculate the size of the solar array.. Two calculations--Minimum solar array based on rate of charge for battery bank, the second based on your loads and hours of sun per day.

First rate of charge. For a short term/emergency backup system, 5% rate of charge can work (especially in a sunny region). Otherwise, 10% to 13% minimum recommended for full time off grid. Batteries are "expensive" and easy to kill--Solar panels are historically "cheap" and having more will keep the battery bank "happier".:
• 12 GC Batteries (2s x 3p strings): 630 AH * 14.5 volts charging * 1/0.77 solar panels+controller deratings * 0.05 rate of charge = 593 Watt array minimum
• 12 GC Batteries (2s x 3p strings): 630 AH * 14.5 volts charging * 1/0.77 solar panels+controller deratings * 0.10 rate of charge = 1,186 Watt array nominal
• 12 GC Batteries (2s x 3p strings): 630 AH * 14.5 volts charging * 1/0.77 solar panels+controller deratings * 0.13 rate of charge = 1,542 Watt array "typical" cost effective maximum
Next size the solar array based on your load and "hours of sun" per day (solar harvest). Fixed array facing south:

### Average Solar Insolation figures

Measured in kWh/m2/day onto a solar panel set at a 72° angle from vertical:
(For best year-round performance)

 Jan Feb Mar Apr May Jun 5.43 5.88 6.29 6.13 6.00 6.49 Jul Aug Sep Oct Nov Dec 6.38 5.86 5.71 5.69 5.25 5.29
Ok--You have "lots of sun" which is good.... Looking at November for minimum sun.
• 1,500 WH per day fridge * 1/0.52 off grid AC system efficiency * 1/5.25 hours of sun per day (Nov) = 549 Watt array November "break even"
Normally, I would be suggesting that your "base loads" (those loads that must run evey day--You cannot "not use" the fridge for a couple days of bad weather (as an example). Typically the base load factor suggested is 65% to 50% of predicted system harvest. Or the array would be:
• 549 Watt array ( 1/0.65 base load factor) = 844 Watt array (65% factor)
• 549 Watt array ( 1/0.50 base load factor) = 1,098 Watt array (50% factor)
While your 4x GC batteries and 600 Watt array could "just keep up" with your typical refrigerator loads--There is no safety factor. For a reliable full off grid system, I would be suggesting around 1,186 Watt array minimum and 6x Golf Cart batteries in 2s x 3p configuration.

The Renogy 2,000 Watt inverter is a bit on the large size--But it should work:

https://www.renogy.com/2000w-12v-pure-sine-wave-inverter/

It is not a particularly efficient inverter with a 2 amp no load draw (P=V*I= 12 volts * 2 amps = 24 Watts). If you run the inverter 24 hours pe day, that becomes:
• 24 Watts * 24 hours per day = 576 WH per day just to turn on the AC inverter
Compared to 1,000 to 1,500 WH per day for the fridge, that is about 1/2 of your fridge's energy usage... And bumps up the overall energy usage:
• 1,500 WH fridge + 576 WH inverter = 2,076 WH per day
• 2,076 WH per day * 1/0.85 inverter eff * 2 days storage * 1/0.50 max discharge * 1/12 volt battery bank = 814 AH @ 12 volt battery bank
• 2,076 WH per day * 1/0.52 off grid system eff * 1/5.25 hours of sun per day (Nov) = 760 Watt array Nov break even
• 760 Watt array * 1/0.65 base load factor = 1,170 Watt array (65% base load factor)
So even a 630 AH @ 12 volt battery bank is still on the small side because of the AC inverter's "tare losses" (24 watt * 24 hours per day losses).

When you add everything together--Too small battery bank, solar array at minimum size, etc. -- Just not a large enough system.

For the larger solar array (1,186 Watts), generally an MPPT type charge controller is a better fit... And you can purchase less expensive "large format" (typically 200 Watts or larger) solar panels (cheaper \$\$\$/Watt than smaller "12 volt" solar panels).

Before you purchase any more hardware--Get a Kill-a-Watt type energy meter and measure the actually 24 hour energy usage of your refrigerator--The one you have may use more or less energy than the 1,500 Watt*Hours I used above:

https://www.amazon.com/s?k=kill+a+watt+meter&ref=nb_sb_noss

-Bill

Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset

Your present battery bank and solar array (420 AH @ 12 volts and 600 Watt array)--Your battery bank should sort of keep up in good weather...
• 1,500 Watt*Hour per day fridge + 575 WH per day Inverter = 2,075 WH per day load
• 2,075 WH per day * 1/12 volt battery bank = 173 AH per day load
So, your batteries should be able to last > 1 day even without solar charging... Wiring issues, batteries not good quality, solar panels not charging correctly, fridge using more than 1,500 WH per day, etc. are all possible issues.

So--We either "debug" your present system--Or "start over" with a larger system. Getting a hydrometer to monitor your batteries and an AC+DC Current Clamp DMM (digital multimeter)-Basic tools for off grid power, and a Kill-a-Watt type energy meter (measure your 120 VAC loads) is a good starting point... You have a system, and debugging/understanding/learning how it works and how to maintain it before you buy a whole new set of solar equipment is not a bad idea...

https://www.solar-electric.com/search/?q=hydrometer (classic glass hydrometer, or nicer dial type meter)
https://www.amazon.com/UNI-T-Digital-Handheld-Resistance-Capacitance/dp/B0188WD1NE ("good enough" inexpensive meter)
https://www.amazon.com/gp/product/B019CY4FB4 (nicer mid-priced meter)

Of course, this also depends on your "interests"... If you are not into electrical/wiring/etc. -- This may be more than you want to tackle... Finding a knowledgeable friend/family member/neighbor to help can also make the project easier.

I have not talked about your wind system yet... Personally, I don't really believe in small wind systems. Few people live where it is windy enough to run the wind turbine (pretty much has to be a "miserable" windy location) and few wind turbines generate anywhere near their advertised output. Add that turbines need to be on a >=30 foot tall tower above any local obstructions for "clear air" (above houses, trees, at top of hill)--It is rare that you can get a good installation in a residential neighborhood. And, you probably want to "tie off" the blades on the turbine prior to a hurricane blowing through. And you want to make sure your solar array racking is well designed and bolted down so you don't lose that too.

You are jumping into a good size project here... All the pieces have to be done "correctly" for them to do what you need. And it will not be "cheap".

If you are looking for a few days/week of backup power--A Honda eu2200i (or similar) inverter-generator and 10-20 gallons of stored gasoline (with fuel preservative) is not a bad solution (it is what I do--But multi-day outages happen a couple times in 60 years for me--So far, this is California and famous for the "hold my beer" method of doing things/failures here).

If you want weeks to months of off grid refrigerator power--You are designing and building a "true" off grid power system--And you have to have a system large enough to carry the loads (variable fridge loads--New food from store, making ice, etc.), and ride through a day or two of cloudy/bad weather.

This is not a trivial design and installation. Really want to do the "paper design" first (really multiple paper designs) to size the system. Then you have to do the physical paper design (the exact panels, charge controller, AC inverter, battery bank, etc.) before buying (any more) hardware. There are a lot of issues that need to be addressed when putting a system together. And a lot of pencil work on costs (solar panels, batteries, etc. which brand/model/size, etc.). Your system is getting large enough where you should be looking at solar/industrial batteries as the golf cat batteries are a bit on the small side... Or even a 24 VDC battery bus (yea, new AC inverter) to better utilize the GC batteries (I do not suggest placing a lot of batteries in parallel--That has other cost/maintenance/reliability issues).

Is this helping? Please feel free to ask more questions and correct me on my guesses/assumptions. This is a good size project to jump into with both feet. And we have not talked about fuses/circuit breakers, size of copper wiring, etc. yet...

One member here "2manytoyz" has documented his solar DIY adventure... Take a look at his website so you can get an idea of the wiring/system and how it connects together (scroll 1/2 way down page):

http://2manytoyz.com/

-Bill
Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
• Solar Expert Posts: 6,006 ✭✭✭✭✭
I understand you don't want a reply from me...
...though I've run a fridge on an off grid system for many years...

First thing is the battery wiring is incorrect. For batteries in parallel,  they should be wired so that they have as close to equal resistance between the cells as possible. So it should be wired like this;

SmartGauge Electronics - Interconnecting multiple batteries to form one larger bank

PeteinPR said;
I have 4 Sam's Club 6 volt GC batteries that are flooded cell deep cycle lead acid batteries. The fridge that I want to operate is full size 120 VAC Energy Star typical refrigerator, with the name plate showing 6.5 Amps.
So it's difficult to know how much energy the fridge draws. It will vary with the environment the fridge is in, how often it's opened, how full it's kept and other factors. These all effect the duty cycle, or how often the compressor runs. The fridge will only draw the max 6.5 amps at 120 volts during the defrost cycle. If you want to get a real idea of how much energy the fridge uses you can plug it in using a Kill-A-Watt meter. They might be available locally through a building supply company or even WalMart.

Another way to get something of an idea would be to look up the energy star numbers and work their annual use back to a daily rate. Though in a hotter environment expect the fridge to use more energy!

So looks like you already have the wind turbine and 600 watt array connected?

So does the charge controller show charging? Typically you would leave the wind turbine and the solar array connected and allow the charge controller to monitor the charge level of the battery bank. Should be no reason to disconnect the charging systems from the battery bank.

So you
PeteinPR said:
....but I am not getting anymore than 10 hours of life before I hit 50% battery alarm.
So what 'alarm' is this and where is it coming from? Have you programed your inverter to shut down at a higher voltage that it's normal alarm and protection for low voltage, which is designed to protect the inverter? What do you have this voltage alarm set at?

Other things can effect the system voltage, including high energy draw, and too small wiring to the inverter.

Home system 4000 watt (Evergreen) array standing, with 2 Midnite Classic Lites,  Midnite E-panel, Magnum MS4024, Prosine 1800(now backup) and Exeltech 1100(former backup...lol), 660 ah 24v Forklift battery(now 10 years old). Off grid for 20 years (if I include 8 months on a bicycle).
- Assorted other systems, pieces and to many panels in the closet to not do more projects.
• Solar Expert Posts: 3,854 ✭✭✭✭✭✭
Real world monitoring will reveal the refrigerator's true energy consumption because rated figures are dependent on controlled conditions, higher ambient temperatures will increase the amount consumed. The 28 days  recorded in the image below demonstrate the effect, the lower results are for days of normal 30°C, the higher were during hotter days, the refrigerators rated 1kWh per day is consistent with the results on normal  days, but could be ~40% higher when ambient is at 36°C.

1500W, 6× Schutten 250W Poly panels , Schneider MPPT 60 150 CC, Schneider SW 2524 inverter, 400Ah LFP 24V nominal battery with Battery Bodyguard BMS
Second system 1890W  3 × 300W No name brand poly, 3×330 Sunsolar Poly panels, Morningstar TS 60 PWM controller, no name 2000W inverter 400Ah LFP 24V nominal battery with Daly BMS, used for water pumping and day time air conditioning.
5Kw Yanmar clone single cylinder air cooled diesel generator for rare emergency charging and welding.
• Solar Expert Posts: 1,147 ✭✭✭✭
That graph provides a great reference point.
I always have more questions than answers. That's the nature of life.
• Registered Users Posts: 3
Thank you guys for all the information. I will order a couple of these items to start the debuggin process. Looks like I need 2 more batteries for sure and about 500watts of more solar panels.

Also, thank you for the wiring instructions on my batteries. To answer the other questions:

- the alarm on my inverter is going off automaticlly when the power shows 50% life, not sure how to correct that.

- I am trying to keep the fridge off grid

- GC batteries can be used to 20% battery life? not just 50%
Not sure exactly what your question is: - GC batteries can be used to 20% battery life? not just 50%

If you are are asking can you discharge the battery bank to 20% state of charge--Yes, lead acid batteries can be discharged that low and still "survive"... However, they must be quickly recharged to >80% state of charge and not allowed to sit for even 24 hours at 20% SoC. The batteries will sulfate and lose capacity if not recharged within hours.

And, the batteries--If, for example rated to 1,000 Cycles at 50% discharge, they will probably have closer to 500 cycle life or less if discharged to 20% SoC.

Another issue is that is it hard to recharge a lead acid battery bank, with just solar, in 1 day... The sun is just not in the sky long enough to bring the bank from 20% to 100% SoC in the ~14 hours (just a guess) in one day without the help of a genset... The batteries just need those Hours on Charge to fully recover.

Another issue is that most rechargeable battery chemistries do not like going "dead", and if discharging continues, the other cells acxtually begin to "reverse charge" the weak/zero charge cells (the cell voltage goes from roughly 2.0 volts to zero volts to -2.0 volts). This will destroy a lead acid cell/battery. That is why a 20% "floor" is suggested--To prevent permanently damaging one or more cells in a battery bank... The going to zero and reverse charging is more likely to happen on the higher voltage battery banks--Especially the 48 volt banks (one 2 volt cell going "dead" will not shut down an AC inverter).

So--If you have an emergency--Yes, you can take the battery down to 20% SoC (somebody hurt, need lighting & power tools to repair storm damage, etc.)==Yep do it.

However, do not plan on running a full time off grid power system this way... For "optimal operation" (longer battery life, less "fussing, monitoring ,and managing of loads", plan on daily 25% discharge (to 75% of state of charge) for normal usage... 50% discharge for those several days of "no sun" during stormy weather. And 20% state of discharge when you have no other choice.

Golf Cart type batteries are not known for long life... Probably in the range of 3-5 years. And hot weather (hot battery banks) age faster... For every 10C/18F over room temperature, the batteries will have 1/2 their life... 75F+18F=93F -- That would mean a battery with 5 years of general life, will die in ~2.5 years.

Using flooded cell/deep cycle GC batteries for smaller systems--They are cheap(er) and relatively forgiving. As the system gets bigger (more AH), then need to look ar larger AH capacity batteries (or even 2 volt cells) for longer and more reliable long term operation. For larger systems, don't just keep adding more GC batteries in parallel... It is a lot of "extra" maintenance.

Regarding the AC inverter--You probably will not be the first person to open the case and cut out the beeper... Things to double check include using a DC Voltmeter to measure the voltage at the DC input to the AC inverter. If your DC cables are too small of diameter (not enough copper) and/or too long, you could have a good size voltage drop from the battery bank to the AC inverter's DC input. Short/heavy cables and good bolted up connections are required--Especially for a 12 volt system. I would suggest that you see no more than 0.5 volt drop from battery bus to AC inverter's DC input under full load.

But at this point, a small battery bank, small solar array, and relatively large/inefficient AC inverter is part of the problem. Running to 50% of battery capacity is not great for long term system operation.

To setup the system for full time off grid refrigerator use--It needs to be larger (array, battery bank, etc.). And you need to budget battery replacement every 3-5 years (especially if GC or similar batteries are used). Even if you only use the batteries for emergency backup (float service)--They do age and eventually fail--Especially in hot climates (keep battery room as cool as possible, if you have a basement--Keeping batteries below ground level--With good ventilation--Helps too). Keep an eye on the batteries--Take Specific Gravity measurements+Voltage per battery, and log to a notebook. You are looking for "differences"... Too low or too high of voltage across one battery, one cell with low SG or all cells with low SG, etc. indicate further research and checking of connections required.

It is just the nature of the beast.

-Bill
Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset