4S2P 560Ah 12V bank with EVE cells - 1 cell failed. What to do next?

[Hewee]

I have a 4S2P 560Ah 12V EVE bank on my sailboat with REC-BMS + Victron that I installed in 2021.

I ordered 8pcs of EVE cells, and noticed that one cell behaved abit different and marked it when I was top balancing. I installed everything nicely in the boat and everything worked great for 2 seasons.

This year the BMS started having problems with balancing the fourth cell (containing the marked cell and one ordinary), it filled up much quicker than any other cells. I decided to lower the upper voltage when charging. One evening we heard a strange sound, later in the evening we noticed a strange smell and I quickly noticed that the marked cell was having a sound when charging. So it was basically boiling, releasing gases. I killed the charging. The cell is intact from the outside when inspecting.

The next day I halved the battery bank to 4S1P with 280Ah, and I'm missing the extra capacity.

So now the summer sailing is over and I'm thinking what to do next. I contacted the Alibaba seller, which was very helpful but said they don't have any matching cells anymore, please buy a new set for a special price. They said the the sold cells are balanced within 3Ah, and new cells are with higher capacity.

So my options are

• Be happy with the 280Ah bank
• Buy 9 new 310Ah cells for a 'special price'
• Try to find a matching cell on Ebay, except nobody capacity tests them.

Obviously the last option is the cheapest and most interesting. I took one cell and testing the exact capacity of it at the moment, and will land somewhere around 280Ah. New 280Ah cells are more close to 290Ah according to the Alibaba seller..

What problems may occur, if I cannot find a matching cell, so one cell may be constructed with 280Ah + 290Ah battery.

Cell 1: 280Ah + 280Ah
Cell 2: 280Ah + 280Ah
Cell 3: 280Ah + 280Ah
Cell 4: 280Ah + 290Ah

Is it a really bad idea?

Thanks!

 

[740GLE]

280 cells are pretty “bread and butter”. I’d source a single cell with the hopes that it’s stronger than your other 7.

Then you’d just have one stronger cell group than the other 3.

Is there an option to break out to individual two 4S groups? Two BMS? That’s another option as well, but buying two REC is not cheap.

 

[Hewee]

Ok, so it's quite safe to buy a newer cell with a higher capacity?

REC is not cheap, so I will not go with two battery packs, which would be ideal. I bought a Wakespeed WS500, so I will have better charging next year from the engine, instead of DC-DC chargers.

What I'll probably do is test all the cells in the winter for capacity and try to match all 2P cells with the same amount of amp hours.