I been researching how to balance my 110ah 4s20p lifepo4, one of the cells always drifts off balance. These were all new cells when I bought them.
So far the bms 60ma balancing wont do the job even when I'm charging the pack at less then 2 amps. I found some balance modules that bleed at 1.4 amps but that would limit your max charge rate to about 5 amps.
These are like 7 dollars each from us suppliers, you need one for each cell. From china they cost 3 dollars each but the shipping can be expensive, for 12 units shipping alone would be 35 dollars. They have these available for lifepo4 and li-ion cells. If you charge at a low rate and the battery isnt too far out of balance these might help.
Another balance module that I think I will be getting can balance at 6 amps (peak 10 amps), these are available from electriccarpartscompany, they ain't cheap a 4s module will cost 80 dollars plus 10 dollars shipping. this module instead of bleeding and wasting the energy, actually takes from the high cell and transfers it to the low cells. They are always balancing while charging and discharging, they suppose to keep the voltage difference between cells to less then 10mv. According to the website you can add as many modules as you need for you battery pack. This would work good on a very out of balance pack and higher charge rates.
all the other balancers , bleed the amps at too low of rate to make any difference.
What if one cell goes bad in your massive battery pack? if you put fuses on every cell, if one goes bad that fuse will blow and take that 1x cell off the pack. If each individual cell was 5 amps, your battery pack will lose 5 amps capacity. The pack will still be fully operational just minus 5 amps. As long as you have good balancing modules it should keep the pack balanced.