Can a battery bank be tested with a multimeter?

[Simi 60]

There are signs we are having issues with our 8x220ah AGM battery bank.

Initially I put it down to an age thing being into their 5th year of 24/7 usage
I also put it down to a winter thing, dark mornings, early evenings = less sun
So ignored it

SOC doesn't seem to be off, always at around 85% capacity and 180ah down in the morning
Batteries get charged via sun and or genset every day to get back to 100% by lunchtime and mid afternoon we usually see around 28.8 to 29v
But the voltage alarms have been kicking off at 23v every morning recently

Power to the many 240v fridge freezers is stable, never has the power dropped out as fridge freezers cut in and out.

Measuring the voltage of each battery whilst connected and underload in the morning shows variances between 12.4 and 11.3v
After charging all show at around 12.7

So, I have now started giving the batts a tickle up with genset at around 6pm - this has batts still showing 24+v in the morning but of course is masking the problem.

Our problem is we are full time cruisers actually out here so calling in an electrician is not really an option.
We are due to come out in Nov so was hoping it could be band aided until then but maybe not.

I was thinking if I could find the troublemaker battery, hopefully no more than 1 or 2 we could make a 6 battery system that would keep us going but tools at hand are a multimeter and a very basic load tester.

OR, should we just keep doing what we are doing leaving all batts in place?

[Alan Mighty]

Originally Posted by Simi 60

I was thinking if I could find the troublemaker battery, hopefully no more than 1 or 2 we could make a 6 battery system that would keep us going but tools at hand are a multimeter and a very basic load tester.

Sealed batteries (AGM, Gel) rule out specific gravity testing of the electrolyte.

Next simplest is open circuit voltage testing:

1. with engine off, switch off everything (master isolation switch). Disconnect cables to the buses (because bilge pump etc may bypass the isolation switch). Disconnect cables to each battery.

2. Let the battery bank sit for at least one hour (preferably two).

3. If each battery does not already have a number, use the time to identify each battery.

4. Clean each terminal while you are waiting.

5. with a digital multimeter set to DC voltage, measure the open circuit voltage of each battery. Record it. Measure again. And record the second reading too.

Note: the voltage difference between a fully charged battery and a half-charged battery can be tiny - in the order of 0.4 to 0.5 volt. A difference of 0.8 to 1.0 volt suggests a serious problem with either the battery, the cleanliness of its terminals, or both. That's why you need a digital multimeter, not an analogue meter. You need a multimeter that gives you voltage to several decimal points. And it must be reliable - that's why you measure at least twice.

[Alan Mighty]

From Nigel Calder:

[Alan Mighty]

And if you find one or perhaps two batteries that measure open circuit voltage lower than the rest of your bank, you re-establish your battery bank and leave that one or two batteries out of the circuit.

Then you can test the open circuit voltage of that one or two suspect batteries again after 5 hours.

If you remain suspect of that one or two batteries, you dinghy them ashore and take them to a retailer such as Century Batteries.

At Century Batteries, you ask if they have a conductance meter and will they please check these batteries. Watch carefully ... a conductance meter only works if the operator first programs into the conductance meter (1) the battery chemistry (e.g. AGM); and (2) the amp-hour rating of the battery (the operator might ask for the Cold Cranking Amps rating, but you reply that your battery is a deep cycle battery, not a starting battery).

Ask politely about the conductance meter. The only brand I've heard of that is reliable is Midtronics. The price is high, to the point that a battery retailer can afford, but lesser mortals cannot (see: https://www.centurybatteries.com.au/...s-brochure.pdf).

After the Century Battery person has shown you the conductance test, then suck your teeth and say that you'll have to speak to your boss about raising the funds for a new battery bank (because it makes sense only to replace the full bank, every one of them, at one time). No point just replacing one or two batts.

[smac999]

Originally Posted by Simi 60

SOC doesn't seem to be off, always at around 85% capacity and 180ah down in the morning

The ah and Soc of the gauge will always drop the same No mater the condition of the batteries. Unless you reprogram the battery size. It’s simple math 180ah of 880ah (what Yiu programed) is 80% . it proves nothing. The batteries could be brand new or total garbage. The meter is still going to tell you the battery is 85% at -180ah because you told it you had 880ah.

You need to look at the voltage when it says 85%. If your morning is -180ah and 23v the bank is shot. Because 23v is ~30% not 85%. That means your 880ah bank is now only ~260ah. If You reprogram the battery Monitor to a 260ah bank then the soc would be correct again.

Measuring the voltage of each battery whilst connected and underload in the morning shows variances between 12.4 and 11.3v

Your batteries are shot.

[Sternwake]

Do you have an IR temp gun?

If so, Check the temp of the connections on those batteries you measured reading lower than the others. When charging or discharging at higher rates, those lower voltage batteries, shoot the IR gun all around the battery, see if any one or two cells is way out of whack with all the others.

Remove those and let them rest and watch how quickly their voltage tanks See if the remaining bank performs better without them.

With one of my previous flooded group 31's, that started behaving poorly, voltage retention/ morning voltage wise, the IR gun revealed the bottom of one cell closest to the negative terminal, was 15 degrees hotter than any other part of the battery when it reached absorption via solar.

The hydrometer revealed that cell would never again exceed 1.255 and only achieved that with extended absorptions which made all cells fizz disturbingly, and 2 weeks earlier, last I dipped that cell, the Hydrometer it was 1.270, so it was rather sudden that that one cell took a kick in the groin, and would have been difficult to notice, and cause me to investigate, if it were in parallel with others.

I removed the battery from regular deep cycling service, Shallow discharges in workshop duty only, and waited 3 more years for it to completely short that cell. I used it for a core charge, before it ever did, but it sure stunk like burning rotten eggs when charging, used tons of water, and required about 150% the juice taken out of it before the one cell reached 1.255 long after the other 5 cells reached 1.275.


If That battery were parallelled with other batteries and kept so, it would have gobbled up the health of the others.
==--

Your statement that your solar has the battery bank at float by midday speaks volumes, Not that your system is working well, but that the absorption times are not long enough.

New batteries might only require 2 hours in absorption with a given solar wattage ratio before amps at absorption taper to the prescribed full level, but at 4 years that time needed in absorption has likely doubled, and AGMS,, really seem to get ticked off and lose capacity faster and faster, and take longer and longer to reach high states of charge, when the controller says 98% SOC is 'just fine', day after day

Most people who claim that solar has their lead acid batteries full by noon, are delusional, and the few who are not, likely run their engines at sunup, and have newer healthy batteries that were not discharged very much the night before, as well as a high wattage/AH ratio, in a lower latitude sunny environment.

Just because the controller switches to float, does not mean the batteries are full, it only means that the controller has decided to no longer hold absorption voltage.
The green light on so called 'smart' chargers, often mocks the human who believes it means the battery is full.

[Simi 60]

Originally Posted by Sternwake

Do you have an IR temp gun?

If so, Check the temp of the connections on those batteries you measured reading lower than the others. When charging or discharging at higher rates, those lower voltage batteries, shoot the IR gun all around the battery, see if any one or two cells is way out of whack with all the others.
.

pretty much same same

Your statement that your solar has the battery bank at float by midday speaks volumes, Not that your system is working well, but that the absorption times are not long enough.

Most people who claim that solar has their lead acid batteries full by noon, are delusional

,
Even when we have 120 amp chargers, 7.5kva gensets and 2500watts of solar?

And that was solar in summer, not winter, I believe I made that point clear.

[Simi 60]

Originally Posted by smac999

.
Your batteries are shot.

Well there is certainly something going on.

If they are shot they and solar are still managing to support a 550 litre fridge freezer, a 120 litre bar fridge, a 100 litre freezer, a 180 litre hot water system, 2 PC's and multiple tv and monitors all running on 240v


On their way out I would say. .

[Simi 60]

Originally Posted by Alan Mighty

If you remain suspect of that one or two batteries, you dinghy them ashore and take them to a retailer such as Century Batteries.

8 X 65 kg lugging out from below, out the back, into a tender and ashore for testing sounds like a lot of effort, especially as I don't have a vehicle.

It's why I mentioned hoping to keep it together until November.
Battery guy comes to us on the hard.
Batteries in and out via battery supplier muscle and forklift.

[rslifkin]

Definitely check each individual battery voltage with the bank under load. That should give you an idea of whether one is bad or if the whole bank just has significant capacity loss.

[Cadence]

Nurse it. As long as the main and gen. have independent start batteries. It sounds like it is battery time as a set for the house bank.

[geoff3nebel]

Yes.
The 11.3 v battery is almost certainly dead.
The 12.4v battery is likely failing fast and not far behind.
Will your bank provide enough to power your domestic appliances with these two disconnected? If yes, I suggest you do disconnect them because leaving failing cells in a bank will drag down the others.
As someone else has posted, when it comes to replacement, change all at the same time, don’t be tempted just to replace the duds

[Cheechako]

Originally Posted by Simi 60

There are signs we are having issues with our 8x220ah AGM battery bank.

Initially I put it down to an age thing being into their 5th year of 24/7 usage
I also put it down to a winter thing, dark mornings, early evenings = less sun
So ignored it

SOC doesn't seem to be off, always at around 85% capacity and 180ah down in the morning
Batteries get charged via sun and or genset every day to get back to 100% by lunchtime and mid afternoon we usually see around 28.8 to 29v
But the voltage alarms have been kicking off at 23v every morning recently

Power to the many 240v fridge freezers is stable, never has the power dropped out as fridge freezers cut in and out.

Measuring the voltage of each battery whilst connected and underload in the morning shows variances between 12.4 and 11.3v
After charging all show at around 12.7

So, I have now started giving the batts a tickle up with genset at around 6pm - this has batts still showing 24+v in the morning but of course is masking the problem.

Our problem is we are full time cruisers actually out here so calling in an electrician is not really an option.
We are due to come out in Nov so was hoping it could be band aided until then but maybe not.

I was thinking if I could find the troublemaker battery, hopefully no more than 1 or 2 we could make a 6 battery system that would keep us going but tools at hand are a multimeter and a very basic load tester.

OR, should we just keep doing what we are doing leaving all batts in place?

Fully charge the batteries. isolate some, all or each from any draw. Check their voltage next am or hours later. If low that's your bad battery or bad bank with one drawing the rest down. Also: If any are hot/quite warm during a strong charge it's a shorted battery.
Obviously (as you are cruising) you may have to isolate one or half at a time to get down to the bad one or two.

[geoff3nebel]

Originally Posted by geoff3nebel

Yes.
The 11.3 v battery is almost certainly dead.
The 12.4v battery is likely failing fast and not far behind.
Will your bank provide enough to power your domestic appliances with these two disconnected? If yes, I suggest you do disconnect them because leaving failing cells in a bank will drag down the others.
As someone else has posted, when it comes to replacement, change all at the same time, don’t be tempted just to replace the duds

I’ve just re-read your post again and realise that when you’ve tested ALL eight the voltages were between 11.3 and 12.4. and only 12.7 when charged, they should be 12.8 to be fully charged.

[geoff3nebel]

Cheechako’s post pretty much sums up what you need to do