Voltage drop in 2 year old battery bank

[Bigbear]

We have been off grid now for over 2 years and up until a couple months ago all was well.  My 8 sump pump (12v) batteries have been doing just fine, but during the last couple months the voltage by moring has dropped off to 12.5 with no load, and 12.4 or 12.3 with load.  The load is nothing more than a light or two, and maybe a small TV, which normally would only drop the voltage down to 12.5 and remain there.  This morning the voltage was 12.4 with nothing being on all night, going into panic mode now.  I checked each battery specific gravity, all showing in the high zone, how can this be, with the voltage only showing 12.4?  I charge the batteries the same every day, solar panels, and when the wood shop is running on the generator, it also runs the battery charger.  In the 2 plus years I have only had to add water to a couple batteries, and that was only in the last 4 months.  Should I panic, or is this voltage drop somewhat normal?  All batteries are connected via + and - buss bars, all connections seem to be tight.  Any help would be appreciated.  Thanks, BEAR

[thirteen]

you might have one cell going bad. Maybe disconnect all of the batteries and check each one for a bad cell or battery. It might be your inverter drawing some power unless you are a total 12v system. You might try and disconnecting the bus bars and let the batteries sit all night then check them. Check them in the morning. That way you would eliminate any thing drawing ghost power. Sound like you have a good system. Just some ideas

[Flux]

Might need a good equalising charge if you haven't done it in 2 years ( assuming wet batteries).

Also disconnect parallel strings and check as Thirteen said to see if there is a weak cell. If sg is up and the same in all then there is probably no serious trouble.

Terminal volts does tend to drop with age but a good equalising keeps things working better for longer.

Flux

[bob g]

the first thing that jumps out at me was your comment "all showed in the high zone"

which indicates to me you have no way to accurately check the specific gravity of those batteries.

it would appear you have a cheapo hydrometer, and you really could benefit from a much better one with a temp compensation chart.

you really need very accurate measurement in order to tell what you have and what needs to be done.

especially if you are going to do an equalization on the cells, which in my opinion you are about 18 months past due for.

get a temp compensation chart and an accurate hydrometer, then check with the battery manufacture to find out what their recommendation for equalization voltage and procedures would be.

don't wait any longer, get after it so you can get those cells back in shape. the longer you wait the more difficult it is going to be to recover the cells.

bob g

[Airstream]

I charge the batteries the same every day, solar panels, and when the wood shop is running on the generator, it also runs the battery charger...

Is the charger temperature compensated?

[chainsaw]

Your lack of water usage sounds very troubling. By all means get a good equalizing charge on your batteries and then check your specific gravity for any significant difference between cells.

I use a 12 (t105) battery bank and water once a week with a single point watering system. There has not been one week these batteries did not take water even with less than ideal solar charging.

[scottsAI]

Bigbear,

I have only had to add water to a couple batteries... in 2 years.

Suggest to me you are not fully charging your batteries with an equalizing charge required at least quarterly. MINIMUM. After each (maybe every other time) water should be required in each battery.

General rule of thumb is every 10 - 12 charge cycles do an equalizing charge.

A cycle is 100% capacity cycle, if 20% discharge daily, in 5 days counts as 1 cycle. Based on this Evey 50 to 60 days an equalizing charge is needed. If cycles are beyond 90 days do it quarterly.

Sulfate is an insulator, restricts battery capacity and voltage can droop, with a high SP it must be thin and battery might recover with a good equalizing charge.

Do to the charging efficiency of lead acid batteries (LAB), you are not getting the battery fully charged daily. LAB charge at 91% efficiency below 80% SOC, this drops to zero by 100% SOC. At 90% SOC the charge efficiency is 50%. 95% SOC around 25% charge efficiency...

As a guess your system is not charging the batteries much above 80% SOC.

Your battery is slowly dieing.

Have fun,

Scott.

[Bigbear]

Thanks for all the input.  I have checked the SP and it still remains high even after resting all night.  My battery charger is a Truecharge 40+.  How high should the equalization voltage be?  When I push the button on the charger for equalization, it never reaches above 14.4 volts and I'm not convinced it is working in this mode.  Today, I have a car type battery charger on the batteries and will let it run for awhile and see if it works.  I don't think it was made for that big of a battery bank, but I will try anyway.  On 2 batteries that I have for a trolling motor, the charger goes up to 15 volts and seems to charge them pretty good.  It is suppose to be a charger that is pulse or something, Schumacher speed charger SC7500.  I have the charger hooked to the buss bars right now, should I try and charge each battery seperate.  Thanks, BEAR  

[scottsAI]

Equalizing charge numbers vary.

Check with battery manufacture for voltage, varies based on battery chemistry.

14.4v sounds like sealed LAB? How long is this voltage held?

Listen to battery: is it making bubbling noise? Vigorously?

If daily battery is charged to 14.4v that could explain why your battery lasted this long without an equalizing charge. 14.4v is getting well into 90's% SOC.

Equalizing charge should last 4 to 8 hours.

Voltage should be above 15v, even as high at 16.2 for 12v battery.

Battery temperature should rise while equalizing charging.

An equalizing charge is a good thing to do 4 times a year, yet not much more.

Equalizing charge is stressful to battery, yet cleans it up and helps last longer.

Have fun,

Scott.

[Bigbear]

Thanks Scott, during the day, my solar will even keep the volts at 14.4 an hour or so, then taper to 13.8.  I always check the batteries, and yes they do bubble, but I guess not to much.  The Morning star that is hooked to the solar panels is suppose to equalize every 30 days, so maybe it has been doing that, and I have never noticed the higher voltage.  I just checked the batteries, and the small charger is now up to 14.7 and hopefully go higher.  How long should I keep it at higher voltage, and could this small charger create and damage to the batteries.  Thanks, BEAR

[scottsAI]

Check the controller as see if set for sealed LAB.

My sealed batteries (from UPS) say charge to 14v unless cycling frequently then can charge to 14.5v. Looks like your controller is set to sealed LAB?

Couple weeks ago. I was charging a 55ah battery. Been sitting for a while, was charging it quarterly. After the first year, load tested had less than 1/3 capacity. Darn. Prior belief was OK to let sit charged for 6 months is wrong.

Charged and tested again. About half. Couple more cycles recovered to 3/4.

Waited a month and tested again. About the same.

While charging with a 15amp charger was charging at 6 amps after 5 hours, battery at 14.9v. Thought this was good maybe complete recovery.

Much later in the evening checked the voltage still at 14.9v still charging at 6 amps... wait a second, battery should have finished charging, realized somethings wrong. Then touched the battery, yikes hot, checked it at 139F several places. Darn, may have fired it. Don't trust charger now.

Never saw the voltage above 14.9v still do not know what happened.

Moral of the story, check battery voltage and temperature while charging!

Small charger.

Watch temperature of battery! And voltage.

Battery should not get hotter than 25F rise. Must keep below 115F. (from Crown battery manual)

If both are within limits do not see how charger can damage it.

Have fun,

Scott.

[Bigbear]

I checked to make sure, but it is set for flooded, and warm batteries, which should be about right.  The small charger finally said (charged) and stopped charging, never did see it go above 14.7.  I have it back on solar charger now, and it seems to be holding at about 14.1 or 14.2, then shuts down to 13.9 for a few, then goes back up to 14.1 or 14.2, but only putting in about 3 or 4 amps.  They should get a good charging, I hope.  Who makes a good battery desulfator?, and do you suggest I get one.  Thanks, BEAR