Help me not kill another battery bank

[rslifkin]

I question the quality of Mastervolt AGMs at this point. There was another recent thread about some dying an early death.

I've got a pair of them (2x L16 6V in series) due for replacement this coming season. They lasted about 2.5 years. They worked great, up until they didn't. After a week long trip with some light PSOC abuse, they were never right again.

They worked fine for the whole trip, but ever since then, judging by voltage drop under load once you draw them down a bit, they've lost somewhere around half of their capacity. Tail current in float has been higher than normal as well, around 0.2 - 0.3 amps after floating for a week, when it used to be less than 0.1 amps. I also noticed one of the 2 batteries in the series pair shows higher voltage when charging and lower voltage when discharging than the other battery, so I'm thinking one of mine is damaged and the other might be fine. But they'll both be replaced.

In my case, I'm not sure I want to spend $2400-ish for 3 of the 4v Firefly L15+ batteries, so I'll probably end up going with either the Fullriver or Rolls AGM L16s as replacements. And add solar to help avoid PSOC abuse, as I have room for about 800w worth of panels.

[crayiii]

May 27, 2018. Installed December 20, 2019

[sailorboy1]

[QUOTE=crayiii;3293112

Resting voltage is difficult while at anchor since we're living on the boat[/QUOTE]

Well i live on my boat and it can do without power for a couple of hours.i suspect you have a bad battery, there is only 1 way to figure out which.

[crayiii]

Originally Posted by sailorboy1

Well i live on my boat and it can do without power for a couple of hours.i suspect you have a bad battery, there is only 1 way to figure out which.

I completely agree with you that to do it right, I need to disconnect the batteries. I agree, there is at least one bad battery since I seem to be only getting about 50ah out of the bank and it happened fairly suddenly. I've heard more bad reports about these 225ah Mastervolts than many other batteries so I've resigned myself to open the wallet and get new batteries.

I just wish I knew what I did wrong.

[Dsanduril]

You have ~18 months between manufacture and install. Unlike FLA, AGM cannot be delivered without electrolyte. That means the dealer needs to keep them charged. Typical self discharge is 2%/month at 20C, 4%/month at 30C. Victron, for instance, recommends storing without charging no longer than a year (at cool temperatures). So, could be that if the dealer/store does not have a charge maintenance program they delivered you batteries that had sat, deeply discharged, for some time and no LA battery likes that.

[sailorboy1]

[QUOTE=crayiii;3293154

I just wish I knew what I did wrong.[/QUOTE]

Probably nothing, batteries go bad. I wouldnt be surprised that you get better capacity by taking a bad battery out of service and running on only 2 batteries.

[Dsanduril]

One other thing, the tail current setting on your controllers seems very low. 2A? I would expect something about that per battery, with 3 batteries in parallel I'd expect 6-7A. For solar this is probably no big deal, the "charger" shuts itself off every night. For wind a little more of a question, but that frequently shuts down at night as well, particularly when at anchor/marina. A shore power charger, however, with the same setting would likely try to keep the batteries at 14.2V forever.

The tail current setting gets even more complicated if you are using electricity while charging, unless the charger has a shunt at the battery to know the charging current it can't differentiate between current being used by your appliances and current going into your batteries. In that case you may need to set tail current a bit higher to account for your lightest load condition + specified battery tail current.

[Chotu]

Originally Posted by crayiii

May 27, 2018. Installed December 20, 2019

I think we might have an answer.

To me, that’s the most likely reason and this is good news. Your firefly batteries will last many years.

[CarlF]

This a classic case of AGM PSOC sulfation damage - the full charge is called a “surface charge” that disappears almost immediately under load. Do some internet searching on “PSOC AGM”.

AGM’s are much more prone to this damage than other chemistries (Flooded, gel , Firefly). In most cases it occurs to cruisers who keep their batteries between 50% and 80% charge. This was the recommended approach with flooded but kills AGM’s in less than a year.

Since your solar apparently achieves a daily 100% charge it seems likely it happened when the batteries were allowed to sit at a low voltage before you bought them. Once it happens, PSOC damage isn’t really reversible although Lifeline has a process for their batteries that helps a little. Remember that the great majority of AGM’s are sold to powerboats who plug into a marina every night or run a genset all night. For them, AGM’s last great.

I’ve had Fireflys for three years after my last set of Lifeline AGM’s lost over 50% of capacity in three years despite lots of care. After three years the Firefly’s still test slightly above new spec.

[SV__Grace]

I feel your pain. We started cruising with newly installed 1200amh of six, 6V Mastervolt AGMs and a year later we were getting low voltage alarms.

After disconnecting all the batteries from the boat and each other and letting them sit awhile, the voltage of 4 of the six was good, and one pair was wonky- not terrible, but the numbers didn't match the others.

So we disconnected that battery pair from the house bank and everything has been fine since.

Some lessons I learned-

1. Solar and wind will raise the voltage so you don't know the real state of the batteries until they are off charging sources, making them appear to be better or more charged than they are.

2. My electrician told me upon installation to be sure to charge them up to 100% at least once a week if not more, which I didn't do as I hated to run the generator for the 8 hours or so that was required to do so. Not charging to 100% often enough appeared to cause the problem. The remaining 4 batteries, 800amh, get charged to 100% using the generator at least twice a week if not more, and only takes 3.5-4 hours. So the lesson is to maintain them by charging to 100% once a week or more and they will perform better and accept charge better.

3. The highly variable partial charging of solar and wind, without getting to 100%, is NOT what AGMs are designed for. If I want to use the generator as little as possible with batteries that charge fast and do well in long periods of partial SOC, then lithium is the way to go, which we will do next year.

[stormalong]

In post 12 you mentioned isolators. Are there diode type output splitters in your system? Are these batteries paralleled or do you switch between them? Do your alternators have external regulators that sense voltage at the batteries?

If you are charging them through isolators and not compensating for the voltage drop you are undercharging the batteries. Isolators are diodes that have about a .6 voltage drop. That is enough to be consistently undercharging the batteries. That coupled with internally regulated alternators means that the batteries are never fully charged.

If you are using isolators as I described you should redesign your charging scheme before replacing the batteries or you will repeat the problem.

[rslifkin]

Originally Posted by SV__Grace

3. The highly variable partial charging of solar and wind, without getting to 100%, is NOT what AGMs are designed for. If I want to use the generator as little as possible with batteries that charge fast and do well in long periods of partial SOC, then lithium is the way to go, which we will do next year.

Unless you can fit enough solar to cover your typical loads and hit 100% most days. That's what I'm aiming for, as even after I add an inverter, my 24 hour consumption should still be well under 150ah (currently it's more like 90 - 100ah). 800w of solar should get the batteries topped back off with no issue and keep generator runtime down to "only when I need it for something", which means an average of 45 - 60 minutes once a day.

[crayiii]

Originally Posted by stormalong

In post 12 you mentioned isolators. Are there diode type output splitters in your system? Are these batteries paralleled or do you switch between them? Do your alternators have external regulators that sense voltage at the batteries?

...

If you are using isolators as I described you should redesign your charging scheme before replacing the batteries or you will repeat the problem.

Each engine alternator goes through a Cristec battery isolator that charges the start batteries and the house bank. I didn't see a voltage drop. No other charge source goes through isolators.

[Cheechako]

Charge them fully, disconnect them (one each night maybe?) and see how it measures before and after.
I found Gel batteries very hard to kill with no care being taken in their charging and usage.
Is it possible you have a draw you are not aware of? Mine drew down to 11-11.5 volts often due to refrigeration.

[Isba]

One battery has a small shortcut inside find it disconnect each battery and measure the voltage and test it with heavy load tester. If not charge every single battery with pulsation charger for some days it will revover to at least 90percent.
I had the same problem. Best Greetings from Austria