Hot off-gassing house batteries?

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ryastu

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Feb 25, 2022
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Being this is my first trawler and experience with larger battery banks, I’m looking for input on whether I’m doing something incorrectly that is reducing the life of the house bank, and will compromise batteries going forward, or whether this sounds like standard end of life for battery bank.
  • Purchased the boat 3- years ago and from the previous owner inherited inverter/charger (Magnum Pure Sine 2810) and house batteries (six, 6-volt Trojan 145 golf cart batteries wired in series-parallel to form a 12-volt bank). Batteries were reportedly purchased 5-years ago (Sept 2019)
  • The system has operated smoothly for the past three years, performed general maintenance from the start, monitoring water levels, keeping batteries clean, and have not changed POs charge settings, and have observed float charge to be a consistent 13.5-volts.
  • Over the past year specifically, and progressing over the last couple months of noticed more and more voltage drop to the point where the battery monitor indicates I’m at 80% capacity, yet the voltage is dropping into the low 11-volt range after an hour or two with pretty low load (< 10amps)
  • I’ve also notices that in the past few months the batteries (specifically the forward pair) have required more DI water than previously to keep them topped,
  • After returning from our trip in September I noted temperature of the forward pair of batteries was elevated when hitting them with a temp gun, temps topped out about 107 degrees (I’m in Alaska so ambient is relatively cool). Temps seemed to cool the following day but were still elevated. The other four batteries, including the battery with the temp sensor were at ambient temperature. I topped all the batteries off with DI water and left for two weeks.
  • Upon returning to the boat, I again noted elevated temps on the forward pair of batteries (in the 90-degree range) and upon inspection of the cells, three of the six cells in the first two batteries were observed to be dry, with water well below plates. I added water, but temps stayed elevated and significant gassing was audible. Wanting to get another 10-day cruise out of the boat I decide to remove that pair of batteries from the system and went forward with a four-battery bank.
  • In the two days prior to leaving port, I monitored the four-battery bank with a temp gun and found battery temps to be at ambient temps.
  • We went cruising for the next ten days and the bank functioned sufficiently, still dealing with relatively quick voltage drop,
  • Upon returning to port and charging them for a day or so, I again heard audible off-gassing. Hit the batteries with a temp gun, and these batteries temps were elevated into high 80’s, with consistent off-gassing.
I’m confused as to why the forward two batteries in the six-battery bank got hot, with the other four batteries at ambient, and then when I removed the forward two batteries, the center two batteries got hot. I should note that while my inverter battery monitor displayed a 13.5-volt float charge. I never did put a multimeter on the batteries to confirm the charge was accurate.

My plan is to replace the entire house bank, but I don’t want to mindlessly go out and purchase new batteries, if there is a problem with the system.

Thanks for your input! -Ryan
 

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You may have shorted out a battery cell. As open lead acid batteries age, they shed lead off the plates which eventually builds up in the cell until it shorts out. That is my understanding anyway as I have never experienced it. With the shorted cell, it depletes the other batteries as it's the lowest voltage. It also heats up. That battery is toast. If all the batteries are of the same age, many may be nearing that point and the bank should be replaced.

Ted
 
Yep, dead battery in there. You can find which one(s) by pulling all the cables and letting them rest overnight and then check resting voltage. They’re old though, so no sense in putting in only one or two. Put all new in and be done.
 
Just had a thought. You might want to check out your series/parallel wiring scheme to see if you’re using best practice.
 
I agree, lead is sloughing off of the plates and settling down in the bottom and builds up enough to short the plates.

A bit surprising as Trojan GC batteries have extra space below the plates to avoid shorting, but all of the symptoms point to this.

So replace them with the same kind. Should last as much as ten years.

David
 
Check the specific gravity of each cell, see if there's a big difference - which points to a bad cell. Testers are cheap at any auto parts store.
 
Its battery time, replace them all. One or more is dragging the entire bank down. Went through the same issue with my genset battery recently. It was 10 years old so I wasn't surprised it was shot.
And whatever you do don't continue to charge a off gassing battery, it's a real mess when they go boom... and it can happen.
HW
 
I can tell you the two hot ones are not the problem. They are the ones doing all the work. Still it doesn’t really matter, the whole bank now needs replacing as there are now a combination of dead cells and damaged cells.

Why this happened? Possibly bad luck with a defective cell from the beginning. Possibly too many repeated deep draw downs of the bank. Possibly imbalance of the connections to place batteries in series/parallel.
 
I agree with the assessment. I will add that it is always worthwhile to carefully check your charging system before replacing batteries. That would include cabling configuration and charging voltage program. It is too easy to assume batts are the only problem and damage new (expensive) batteries before you figure out that there may also be a charging problem.
 
Greetings,
Mr. R. I'm a big fan of checking specific gravity (SG) of individual cells on occasion. As Mr. JC notes in his post (#6), any significant difference in readings indicates a bad cell AND the testers are dirt cheap (boat-buck-wise). Needn't be done every time you service the batteries IMO but perhaps every 6 months OR if you think you may have battery issues.
 
At the current Trojan replacement prices, I would be tempted to switch to 100Ah
or so lithiums. They have become cost competitive at the same usable amp-hours.
If the inverter charger can be configured to charge them properly it's a win-win.
 
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