Can a battery bank be tested with a multimeter?

[Cheechako]

Beware that brand new marine batteries I installed in a 24 ft powerboat just before sale measured 12.45 and 12.46 after full charge and sitting all night.

[Simi 60]

Originally Posted by Cheechako

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.

None get warm, I shoot the temps with laser several times a month when doing routine ER checks when underway.

I am pretty sure there are a couple of big breakers hooked to batts prior to inverter charger.
Will be interesting to flick them and see what happens, might possibly still be running everything off of solar.

[Simi 60]

Originally Posted by Simi 60

None get warm, I shoot the temps with laser several times a month when doing routine ER checks when underway.
.

When I say none get warm I should clarify
Under full charging load the ones on the ends get around 27c and the mid point ones get around 28c at terminals
Ambient ER temp was around the same

Batteries now at full charge by 10am showing 28.7v under full load of all refrigeration, tv, two PC and washing machine usage.
You would think it was all working fine.

[sailinglegend]

[QUOTE=Alan Mighty;3437693].....simplest is open circuit voltage testing:

Very good posting but just one correction:

1 ....... Disconnect cables to each battery.

You only need to disconnect the negative (not the positive) on one 24v battery pair at a time - that breaks the circuit for those two batteries and keeps the power going for the boat. Leave for 2 hours before measuring both batteries. If the voltage of one of the 12v pairing is much lower than the other it is definitely dead. Cover negative cables and move to next 24v pairing.

2. .........

[rslifkin]

Originally Posted by Simi 60

When I say none get warm I should clarify
Under full charging load the ones on the ends get around 27c and the mid point ones get around 28c at terminals
Ambient ER temp was around the same

Batteries now at full charge by 10am showing 28.7v under full load of all refrigeration, tv, two PC and washing machine usage.
You would think it was all working fine.

That makes me think you may not find bad batteries per se, just that they're wearing out and have lost enough capacity to be a problem. If that's the case, it's basically the ideal failure mode, as it happens progressively and doesn't just pop up as an issue one day.

[AMCarter3]

This is a delayed response, but meant to be helpful. I have a powerboat in a charter fleet of 50 boats in Bellingham, WA (San Juan Sailing & Yachting). One of our frequent maintenance topics is how to best maintain AGM batteries. While we don't have THE definitive answer, we have had some interesting success doing a periodic deep cycle process. Here's how one of our owner's did it:


On Illumine I have a solar panel and AGM batteries. Over the last three years I have had two sets of batteries go bad. Each of these sets lasted about one year, way shorter than expected. We have had trouble figuring out the cause, but recently I think we found it. It appears AGMs like to be charged hard, with high amperage at or above 15% of the amp-hour rating of the bank. For example, my bank has 500 amp-hours so should be charged with at least 75 amps.

This is all well and good but solar panels charge at a much lower rate, 5-20 amps. In addition, the solar panels usually do most of the charging in the early mornings before the boat gets under way. So the batteries seldom get charged hard. It appears this causes sulfate ions to build up on one side of the barrier between the anode and cathode. Charging hard has the power to move them back.

Just last week I ran a test on my batteries because I was noticing they seemed to be dying again. I ran a constant load on them for 5 hours – during this test they dropped from 13.1 to 12.3 volts. This was definitely short of their expected capability. I continued to draw them down all night and by morning they were at 11.8 volts.

I then plugged the charger and solar panel in and charged them with about 80 amps. It took all day and the next night to charge them fully. I then unplugged the charger and solar panel again and put on a 10 amp load again. After 6 hours the voltage dropped from 13.1 to 12.6 – much better. I then left the load on all night again and by morning the voltage was at 12.45 – again showing normal or better performance.

So, long story short, for those of you with AGM batteries I would suggest running them down below 12 volts and them charging them hard at least once every couple of months. Under some circumstances this may be happening regularly due to your boat’s situation. But if your AGMs loose oomph early try this to see if they can be resurrected.

[LargeMarge]

Originally Posted by smac999

.
[snip]
...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...
.
[snip]
.

.
I read '8x220', or about 1,760.
.
BTB, on our ExpeditionVehicle, we installed Concorde Lifeline AGM in 2003.
Six 105ah (a total of 630ah?).
We rarely empty them past 97% (ninety-seven percent).
After nearly two decades, our bank shows no signs of senility.

[NPCampbell]

Originally Posted by Simi 60

Batteries now at full charge by 10am showing 28.7v under full load of all refrigeration, tv, two PC and washing machine usage.
You would think it was all working fine.

28.7v is the voltage of your charging system, not of your batteries, no?

Have you increased your electrical load? Could you be depriving your batteries of a full saturation charge? Your absorption phase could be too short. Do you see the current into your batteries drop noticeably during the float phase?

Do you routinely rely on the lower current output of your solar to charge your batteries? If you don't provide your batteries enough current during the bulk charging phase then you may not be completely reversing the sulfation buildup between charges.

Does your charger have an equalization mode? If sulfation is causing lower output of some cells, equalization may be able to reverse it.

[Sternwake]

My experience in closely monitoring the voltage trends and tendencies with a group 27 TPPL AGM throughout its 6 year/~1200 deep cycle lifespan, very much favor the high amp both retaining and returning battery performance.

I judge this by comparing the voltage retention, for AH removed under X amount of load, during subsequent cycles. While some variables exist each cycle, the trend is Strikingly obvious with enough viewings of monitor during discharge.

Its group 31 replacement also responds in kind. Once it appears that before bed or morning voltage is lower than expected/hoped for. The next night I take it even lower, amp hour from full wise, and start a high amp charging source before the solar can do anything.

40 amps per 90AH of group 27 Northstar TPPL AGM seemed much more effective than just 20 amps, and this was most effective when that amperage was applied before the solar had begun contributing anything.

It seemed more effective when I would intentionally draw the bank lower and start the high amperage before sun got much above the horizon.

With nearly unlimited charging amperage potential, how many amps it takes to instantly reach absorption voltage, from 50% level of depletion, or less, is also a great indicator of battery health, in my experience. Even a few hours of morning sun can really diminish the 'quench amperage' required to instantly reach absorption voltage, and the lower the 'quench amperage' needed, the less effective the higher amp charging source applied seems to be in returning performance.

My group 31 Northstar TPPl AGM, when ~20 cycles old gobbled up 134 amps for several minutes before reaching 14.7v at battery terminals, but now at Cycle number 300 or so, 94 amps can do the same from the same level of depeletion. AH wise, not % of original capacity wise.


More recently I got 4 Deka Intimidator gc-2s AGM's for free. 4 years old but minimal cycles accumulated and mostly floated 0.2v above their recommended before I got them. I was not sure of their remaining health /capacity before employing them in my system. I only knew they were holding 12.4v under a 45 amps of inverter load for several minutes before I replaced them on a friends vessel, with 8 new lifelines and 2/0.

Employing just 2 of these 190 ah agms, they do not perform as well, voltage retention wise, as a 300 deep cycle accumulated 100Ah TPPL AGM, until ~65Ah from full.

They also seem to lose their voltage retention ability when lower and slower solar makes up the bulk of their recharging, even when their tail amps reach the required threshold I set, before late afternoon.
While these Deka's say no more than a 30% charge rate, I can and do greatly exceed that when they seem to be misbehaving, voltage retention wise.

I am a big believer in the occasional high amp recharge from a well depleted state on AGMS and to a lesser extent, flooded, but especially so in PSOC duty. Its not just that higher rates bring the battery to a higher SOC before the next discharge cycle begins, but the higher rate itself is somehow beneficial, perhaps forcing the electrolyte more thoroughly through glass matting and deeper into the plates and the heating druring high rate recharging helping to dissolve the sulfation.

The increased voltage retention afterwards cannot just be from the battery retaining more heat on that subsequent discharge, as the subsequent cycles with more normal battery temperatures, are also improved, though will walk down as expected, until the next high amp blast.

This is easily repeatable. Depending on before bed voltage, and morning before solar voltage, I will do the high amp recharge from a well depleted state, as often as 7 to 10 deep cycles when working the bank hard, and upto every 30 cycles if I am not depleting it as much, AH wise, overnight, for whatever reason, usually determined by amount of laptop usage

The 30% limited AGMS, as opposed to Lifeline and TPPL AGMS which basically say no amperage limit, still, in my opinion, benefit from the occassional high amp recharge from a well depleted state. I will exceed 30%, and just monitor battery temp rise, and they will rise in temp, and do so faster with more cycles accumulated as they age.

When significant heating during charging at a 30% + rate occurs, I limit the duration by lowering voltage delta of power supply during bulk, and then choose absorption voltage based on battery temperature, but still aim for bulk amps to be in the 30% rate in 80f or below ambients and as long as the battery is still relatively healthy. When less so, they heat to a much greater extent, and I am more timid in the amperage I allow them, or the duration I allow it. Takes 10 seconds to set the timer on my phone so I don't forget.

In my opinion, low and slow 'trickle charging' as always being best is something that should only be spoken about flooded automotive starting batteries, by those grasping at antiquated advice, when recharge time is not a factor, and true full cannot ever be determined anyway, by the neurons at hand, and the tools available.

Restoring lost capacity is never as effective as preventing its premature decline to begin with. I view the high amp recharge from a well depleted state is the best way, to prevent premature capacity loss of AGMS, in my usage, where reaching 'true full' is often realized, just often at a max of 10 to 13% rate instead of the ~130% rate i can muster when I feel it will be beneficial.

Before I acquired high amperage adjustable voltage manually controlled charging sources, in addition to the solar, my strategy evolved to, was less capacity drawn deeper.
$ per cycle ratio improved with lesser capacity in my usage with flooded batteries, and I attribute a good portion of that improvement, to an overall higher charging rate, and my first AGM performed so much better after I was able to feed it a high rate from a well depleted state that it is my Go to procedure when before bed or pre solar morning voltage, disappoints.

[Simi 60]

Most of this was answered in prior posts

Originally Posted by NPCampbell

28.7v is the voltage of your charging system, not of your batteries, no?

No, its the voltage of batts when amps are pumping in

Have you increased your electrical load?

No

Could you be depriving your batteries of a full saturation charge?

No

Your absorption phase could be too short.

No

Do you see the current into your batteries drop noticeably during the float phase?

Amps into them? Yes

Do you routinely rely on the lower current output of your solar to charge your batteries?

I have 2500 watts of solar
In summer they routinely see 80+ amps

If you don't provide your batteries enough current during the bulk charging phase then you may not be completely reversing the sulfation buildup between charges.

They get plenty of amps

Does your charger have an equalization mode? If sulfation is causing lower output of some cells, equalization may be able to reverse it.

They are AGM
Only lifeline batteries mention the need and then only if batteries never got full charge, which ours always do, EVERY DAY

Lifeline use the term "Conditioning". They say this should only be done when the battery is showing loss of performance due to having spent extended time in a partial or low state of charge, or that don't often get charged above 90% (Cruisers that never come to the dock please take note!)

[Simi 60]

Originally Posted by rslifkin

That makes me think you may not find bad batteries per se, just that they're wearing out and have lost enough capacity to be a problem. If that's the case, it's basically the ideal failure mode, as it happens progressively and doesn't just pop up as an issue one day.

My thoughts as well
Everything still functions fine, they just don't seem as good as they once were so says the numbers on the battery monitor.
Same amp hours used, same SOC but lower voltage in the AM