I saw in the net,that there are a mini car jump starters(very small gadget-relative to the old fashion ones)that can start the car several times with battery capacity of 8000mAh,14000mAh etc..

My question is related to the 12V lithium ion polymer battery that this jump starter has.

If i will buy the 8000mAh jump starter(this model is enough to cars less that 2000CC engines) and i will charge it only to 40% capacity,will it be enough to start the car with totally dead battery(at least one time)?

If not,what is the minimum capacity that the jump starter battery should have in order to be able to start the car at the wrost case(as i mentioned-totally dead battery)?

I know that 40% capacity at 3.7V LI-ION battery is about 3.75V-3.8V(open circuit voltage),What is the OCV value of the a polymer li-ion battery of that jump starter when it has 40% capacity?

My question is based on the fact that while keeping the li-ion batteries in storage the best capacity value for it,is 40%,while more than that into the area of the 100% capacity will speed the degradation of the battery,therefore the day that i will need to use it,the battery might be degraded in such way that it will not be able to start the car(failed battery).

Thanks in advance.