Spare cell considerations in DIY LiFePo4 packs

[Barold]

I am looking to construct a 300Ah battery pack for our sailboat house system - For battery box size considerations I think 8 cells is the limit at this time, unless I build a new box. I am still dubious on the number of cycles these cells will produce and what the failure rate of individual cells so wondering if others consider ordered 'extra' cells as back ups in the event a cell or two fail.

I am looking at the blue aluminum 150Ah cells, so for 300AH, it's 2P4S - If one cell fails the system will continue to limp, but given how much shipping costs can be, would it be prudent to have more cells for back up or go with 100Ah cells and have a 3P4S bank?

Thanks!

 

[MisterSandals]

would it be prudent to have more cells for back up

I am wondering if a new cell can even be substituted into an old group of cells, with good results?

My gut feel says the new cell would not stay in balance well with the older cells. But perhaps the good news is the new cell will not be the first to reach max charge or discharge, but unfortunately be underutilized.

Perhaps regularly rotating the extra cell(s) into the mix would keep all the cells, even any spares, matched.

 

[Sojourner1]

I don't believe having an extra cell is needed. If a cell goes south just replace at that time with a new cell ( benifit of prismatic cells). If that happens to me that's what I'll be doing.

In my years of researching and reading all sorts of forums when this has happened they just changed out that cell, I don't believe I've read more than 2 or 3 times that it has happened.
A properly setup system should last you a very long time. I'm almost 3years 9 months using it everyday never turning the system off (see sig) it truly has been a set it and forget it system (proper safe guards protecting the batteries in place). 500+ full cycles so far.

Here is something for you to read with real life experience.

5 years of CALB LiFePO4 battery operation : Components, Installation And Performance - Energy Matters Forum

Some good info there use their search engine for specifics in that forum.