Will this be installed mass-produced equipment? Or just personal? If it's mass produced, I'd highly recommend using an industry trusted lithium-ion protection IC. At least here in the US, people are getting sued left and right for improper lithium-ion deployment...regardless of which party is actually at fault. Voltage sensing I feel is easy to do correctly with discretes, but over-current (over-discharge), maybe a little more challenging to prove you have a robust solution. Typically those use a timers and delays to check for recovery conditions, etc.