colinfdr avatar image
colinfdr asked

GEL batteries failing after 6 months?


I upgraded my boat batteries and charging system 6 months ago.

6x 220AH GEL diagonal wired in series parallel with carefully identical cable lengths.


Charged with a Multiplus programmed for Victron GEL batteries and set to 70A max charge rate. Monitored with a Smart shunt. 4x95mm cables to the Multi.

System worked great, they have been cycled down to 85-90% about 4 times no problems, then this week, lost shore power and had a voltage alarm at 92%, 22V.

After a full charge to float, I consumed 30A out of them for approx 1.5hr, watching the voltage steadily drop from 26-24.5V as seems typical, then suddenly they 'collapsed' to 22V.

I disconnected them all, charged with a 12V compact multi I have and painstakingly performed steady discharge tests on each single battery, they all perform as expected until about 90%, then the voltage 'collapses'.

I have not seen this behaviour before, any experts out know what might be the cause?

Thanks in advance.

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nickdb avatar image nickdb ♦ commented ·
What multi do you have? Do you have any VRM charts showing the loads they power?

Could you share the multi's config?

Presume these are victron batteries or are they an other?

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colinfdr avatar image colinfdr nickdb ♦ commented ·
Hi, it is a 24/5000/120 multi.

I have not got a Cerbo or CCGX so do not upload to VRM at the moment.

Yes they are Victron batteries.

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3 Answers
janieronen avatar image
janieronen answered ·

Have you measured mid-point voltages during the float and discharge cycle? You mentioned 30A discharge for the bank which means only 10A per string. String voltage should stay over nominal voltage 24VDC until around 50% SOC with that small current. And if all batteries behave identically please connect your distributor. Batteries can be damaged due long shelf time if not maintained properly during warehousing.

Have you checked the manufacturing date from the batteries?

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colinfdr avatar image
colinfdr answered ·

Thank you for responding, I checked the mid points, and they seem well balanced, and the current distribution measures nice and balanced too, I will check on the dates of manufacture.

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kevgermany avatar image kevgermany ♦♦ commented ·
What temperatures are you generally seeing in the battery compartment?
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billt avatar image
billt answered ·

Hi, I experienced a very similar problem. I have 2x265ah Victron gel batteries wired in series. Mastervolt combi 24/2500/60, with mastershunt etc.

Batteries about 3 years old, carefully monitored, never discharged below 70% SOC.

Following first overnighter this season, without shore power, awoken by alarm at 05.00 with batteries at 22.6v. Later in the day. under charge from my Fischer Panda Generator the batteries quickly recovered to a good voltage (very strange?).

Returned to home mooring, Batteries at 100% SOC, 26.73v

I added two remote battery voltage monitors to monitor each battery individually and left shore power off. Left various power drawing products on, eg fridge, TV, and lights and went home.

Following afternoon, Battery voltage at 22.77 with a SOC of 77%.

bluetooth battery monitors show a typical gradual decline of voltage of one of the domestic batteries to a low of 12.66v, whilst the other dramatically fell from 12.6v to 10.1v over the period from 02.00 to 02.30 and remained at around this level for the rest of the night.


the upward spikes are the Mastervolt solar power regulator kicking in.

I assume that one of the cells is failing and am having the batts replaced with a pair of Victron AGM 230ah super cycles on Thursday.

all the best


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