One Bad Battery In House Bank

[sher9016]

I have a house bank consisting of 6 Trojan T-105 batteries plus 1 @ 12 volt battery wired in to supply my 12 volt house bank. The bank is about 7 years old now. One cell in one of the Trojan seems to be bad? Over a period of 20 - 30 days the fluid level drops enough to uncover the plates. The other cells seem alright, only needing to be topped up occasionally.

I understand that adding one new battery into the bank as a replacement will result in that new battery being quickly depleted to the same level as the other batteries, however, the remaining batteries all function fine and I am concerned that leaving the battery with the bad cell will damage the entire bank. I am currently cruising in Colombia SA and the quality of batteries is not that great; also I plan to sail to Portugal in about 2 years and will replace the entire bank then.

My question(s) are:
Will the bad cell damage the other batteries?

Is there another option other than replacement?

Will replacing the one battery likely be sufficient to get me through until I want to replace the entire bank?

Thanks!

[tkeithlu]

Consider the possible option of removing the bad battery from the bank, and then replacing the whole thing when you are in a good place to do so. You'll have less storage capacity, but will be able to protect the bank. You would have to modify your parallel/series arrangement, connecting one six volt to another in parallel, and that might be difficult with the cables on hand.

In any case, do give some thought to a new bank of identical batteries. Concensus on the forum of late has favored the Duracells at Sam's Club prices.

[motion30]

They are six volt batteries assuming a 12 volt system he must remove two batteries in order for this to work. The question is whether four batteries will do the job he needs done

[S/V Illusion]

It’s not hard to rewire five 6 V battery interconnections, two of which are in parallel.

[ikanode]

The bank is about 7 years old now

At that age from my experience, the rest are probably about to fail. They're all old, one just died a little sooner than the next.

I'd test each one individually for their actual Ah capacity and then decide if it's worth replacing just one. You're likely to end up buying 7 batteries in the next few months. One as a short term replacement and then a bank of 6 new matched ones.

[sailcrazy]

FWIW, we operate a very similar system....6 T-105s, connected as 3-12v batts for the house, and a 12v conventional batt for starting either the main eng or the genset. We have used T-105s since I redid the batt system in 2003....we've never gone beyond 6 years on a set of batts. I, too, suspect that your whole bank is about to fail on you, and waiting another 2 yrs to replace may well put you in a bad spot-they'll quit just when you really need them. I'd look to replace sooner rather than later.

[geoff3nebel]

I’m guessing they’re connected in series parallel to give 12v 675A
I had 4 T105s installed in 2014 and one battery developed a bad cell last summer while I was cruising Biscay. I disconnected it and its ‘partner’ - the other pair are fine. I continued with halved amperage which was ok.
I suggest you do the same - disconnect the dud and its partner. Depending on what your running you might be ok with 4 T105s giving you 450A for the moment. When the day comes you’ll need to replace the lot. Never mix new with old. I’m going to replace mine.

[Scubaseas]

Originally Posted by ikanode

At that age from my experience, the rest are probably about to fail. They're all old, one just died a little sooner than the next.

I'd test each one individually for their actual Ah capacity and then decide if it's worth replacing just one. You're likely to end up buying 7 batteries in the next few months. One as a short term replacement and then a bank of 6 new matched ones.

This. One bad battery will keep your voltage regulator from properly charging the rest of the bank (it will try and overcharge the "good ones if left in the bank) and will also pull the other batteries down when not charging Which makes them all fail sooner than later. Either drop out two batteries or just replace the single bad battery mindful that 7 years on a bank is a long time. I'd just drop one in and see how it goes but prepare to replace the whole bank sooner than later.

[wsmurdoch]

Two years ago on our way to the Bahamas, one of our three 12V batteries in our house bank (another single 12V battery starts the engine) became hot when charging, was using water in one cell, and smelled of overcharged battery. I lifted its black wire to isolate the battery, and we continued along on using the two remaining batteries. When we arrived in Miami, I replaced the one bad battery. I did not replace all of them because the logistics of getting it accomplished were more than I wanted to deal with. At home after five months of operating on two old and one new battery in the house bank, I tested the three batteries both with a carbon pile battery tester and with a West Mountain Computerized Battery Tester (West Mountain Radio - Computerized Battery Analyzer). All three batteries tested good with the carbon pile tester, all could supply a high current for a short period of time. The CBA IV showed that the new battery still had more than its specified A-hr available when discharged at 5A. The two older batteries had about 75% of their specified A-hr available. I replaced all three batteries with three matched batteries and put the battery I bought in Miami in my motorboat. Since then, I have had no problems with the batteries.

[Cheechako]

I have had no issues with replacing one battery in a bank.
I have mixed gel and flooded acid batteries with no apparent problem.
You are better off to take a bad battery out than to leave it in.
Some batteries become shorted and it's very bad to leave it in. This battery will usually be warmer than the others after a good charging.
At 7 years old though, just replacing all is the best answer.

[sailcrazy]

I agree with geoff3nebel and others....get the bad batt out of the system. But if you disconnect a pair and plan to just use a reduced amphr rating, remember that most batt experts (including Trojan) recommend reducing the amphrs avail for each yr of service. I reduce my amphr rating for my batt monitor and charger by about 10% per year. With one pair of T-105s disconnected you will not have 450amphrs remaining to play with!

[SV__Grace]

About a year ago we had one bad battery in a bank of six 6volt batteries.

Once we identified the one with the problem we disconnected it and it's partner from the bank and the remaining four batteries in the bank have been fine since, just have to run the generator more often.

[Emouchet]

You cannot leave the faulty battery connected.
All the others will discharged into it, trying to balance the voltage over the bank.
This will kill the other batteries pretty quickly.

[sher9016]

Thanks everyone. Based on the input from all the years of sailing knowledge represented by you guys and considering that quality is lacking down here (along with a VERY favorable exchange rate) I am going out tomorrow to buy one replacement. If that gets me a year down the road then I am happy. After that year I will have replaced my dinghy with a new AB dinghy and a new outboard and I will have had my framework built to receive my new to me 720 watts of solar, and will be ready to spend a thousand dollars on new batteries. If I don’t make a full year then I can hold off on the dinghy or outboard a few more months.

Thanks for input!!!

[Leee]

You've had some good advice on most of the responses so far. You will have to replace two batteries in a 6V. series/parallel bank.



Same situation here with T105 Trojan 6V. A high failure rate as two of the eight new ones were faulty right off the bat. Ended up having to replace them all in Portugal where we found the price double that of the US and Canada. If you are heading to Europe, try a different brand and try to buy them some place where the VAT is lower than 22%.