First post, by adalbert
Let's say we have a 14,4V Ni-MH laptop battery pack with 12 x 4/3A sized 1,2V Ni-MH cells. They are wired in series and use a dumb charger. There is no balancing circuitry at all. There usually is only one temperature sensor. Voltage may be uneven on some cells, which causes generation of heat until charging is completed. The cells can withstand that, but it decreases their life expectancy. Long-term storage is a problem, because voltage goes out of balance pretty quickly, and when you plug the charger after a period of no use, you are degrading the cells even more, because they are overheating while re-balancing.
Could Ni-MH cells be replaced with 4 x 18650 Li-Ion 3,6V cells? That should provide the same voltage and similar capacity. Obviously they would be connected through BMS charging/balancing circuit.
We should have 2/3 space of the battery pack empty now, so there would be plenty of space for the balancing and charging circuitry. There would be also less cells, so there should be less possible points of failure.
There should be even enough space for a thermal fuse touching the case of each cell. For maximized safety I would also like to use Panasonic 18650 cells with internal "current interruption device".
I don't want to just plug li-ion cells in series and call it a day, I know that this is dumb and a fire hazard. But can it be done the way I described in this post?
//edit: updated the schematic a bit
Repair videos: https://youtu.be/T6mXM1tA7pA