What To Do with Dead / Poor Cell in Bank

[rigormortis]

I have house bank of 4 205 reserve capacity/865 marine cranking amp lead acid batteries (12 volt). Evermaxx (Walmart?). Don't know how old they are but likely better than 5 years and could be 10. Came with the boat and PO refused to talk to me after sale (??!!).
Started to get bad feeling about these batts. I have new Guest charger (5+5) and new solar controller (35 watt) for my solar array (400 watts total).
Brought batteries up to full charge here in Kota Kinabalu, Sutera Harbour Marina (best marina I've ever been in and $27/night for 40 footer).
Turned off all charging and the battery switch to off last night so let them release surface charge.
This morning I did the hydrometer test on all cells. Most cells were reasonable --that is between 1.225-1.250. However one cell was slightly in the red (below1.200) although who can read those cheap turkey baster hydros at the best of times. After repeated testing.
My question: should I take that one battery off line so as to improve performance of other 3 or leave it alone? I have 800 mile sail ahead of me to Singapore where I will buy a new quartet of batts. My engine start batt is new and in fine condition. I cleaned all terminals today and electrolite levels all good.
Or does taking it offline have any effect on the other batts.
Any and all advice appreciated.
Pete

[Nemo55]

Could be and most likely is just a bit of plate sulphation,,,being that it is a non critical system battery, i would leave it alone until you can see your way to de-sulphating the cell.

[TeddyDiver]

Iwould take it of..

[GordMay]

Pete:
Five year old batteries a likely near, or at, their end of life. You should plan to replace them all, soon.

Hydrometer readings of all cells should be at least 1.225, and should show less than 50 points difference between highest and lowest.

An SG difference of less than about 50 points maximum, between highest & lowest reading, may not be critical. In this case a complete re-charge may bring the battery back to useful service.
More than 50 points difference, and I would definitely remove the battery from the bank.

You may want to try a cell to cell voltage test, prior to abandoning that battery.

Take a coat hanger, and make two lead extensions about six inches long, and attach them to the voltmeter’s test leads.
Touch the positive lead to the positive terminal, and stick the negative lead inside the cell next to it. It should read about 2.1 to 2.3 volts.
Now insert the positive lead in the first cell, and the negative lead in the second cell.
Proceed down the line, until you get to the last cell.
Here you will put the positive lead in the last cell, and the negative lead on the negative terminal.
All the cells should read the same, or within 0.2 volts.
If one reads 3.0V or more, you have a shorted cell and the battery is no good.
If you get a very low reading or a zero reading, the cell is open, and again the battery is no good.

Good luck, and best regards,
Gord

[rigormortis]

Thanks Gord, as always.
I can't buy batteries here so will carry on to Singapore and replace the set of 4.
Your system of dipping coat hangers in acid whilst in a confined gaseous, sweaty after cabin sounds interesting, but i am too ascared of sparks and explosions in general.
I will make it to Singsing and throw them under a bus.
Thanks for the tips, though
Pete

[GordMay]

Pete:
I’m not familiar with the Guest 5+5 charger. Have you got a model number?

FWIW: a 5 Amp charger is suitable for a battery (bank) of only about 60 Amp/Hours, whereas a 10A charger will charge a 120 A/Hr battery (bank) in about 12 - 14 hours.
Your 5+5 charger may be way undersized for your 4 battery bank.

[rigormortis]

Hi Gord:
And thanks for the info. I have a Guest model 2611A (5/5 amps) for use with 2 independent 12v batteries. That is, starter and house.
Is this too small for a one starter/4house battery system?
I don't spend too much time in marinas and my solar puts out 15 amps at noon on sunny day.
I am headed to Singapore and will buy new batts there but maybe I should think of a bigger charger?
Pete

[GordMay]

Were I buying (first) new, I’d want a much larger charger for my 4-battery house bank; but if it’s been working for you ...

The Maximum recommended battery (bank) size for the 2611 is up to 200 Amp-Hour for recharging.
➥ http://www.marinco.com/files/support...nuals/2611.pdf

[rigormortis]

Yes, Gord, I think you are correct and I will look for bigger charger whilst in Singsingapore. The 20 amp (10+10) should do my deal.
Thanks again and enjoy the snows.

[btrayfors]

I basically agree with Gord...as usual....except that you said you don't spend much time in marinas, in which case the battery chargers you mention are MUCH too small for that size battery bank.

Problem is that while the small chargers will eventually charge the batteries fully, it will take a very long time.

If you're only going to hook up to shorepower infrequently and/or you plan to power your battery chargers with an onboard generator (fixed or portable), you'll want to have a much larger battery charger. I'd look for one with at least a 40-60 amp output.

Note that start batteries require very little charging, so most charging capacity should be directed at the house batteries.

Good luck on your sail to Singapore. I'm envious.

Selamat djalan!

Bill