So I am new to this and will say that I have done some electrical projects before and am pretty confident with what I am doing. But I will jump to the 'story'. This battery is about 4-7 years old and is dead. And of course I got some new ones and they work great. But anyway I wanted to just kinda experament and replace the cells in the battery pack. They are all 18650 cells. And this is the replacement I wish to get. It seems to be closed to these originals. Before taking apart I charged up what little it could hold and tested a battery. it measure (off top of my head) about 3.8 volts and almost 1 amp. being so old I think they where able to hold more than that. But there is a concern (hence this post). I know that batteries in series adds up voltage, and in parallel it adds amps/current. Does the circuit board control the amps/current because 8A would fry a tool I am sure. And because I fear this I will only replace the top half. Which would add to 7.5Amps! So I am kinda worried about this granted I still want to learn from this. I ordered a Imax b6 (something like that) to really determine some stuff. But how are they doing this because even with these it should be killing the tools. But maybe that is why there is such a "motherboard" to keep this in control. I would love any info on this, it is something I want to accomplish and learn to do. I hope yo all help! My other group (stack echange) let me down, answered with "Li-Ion batteries are dangerous, do not bother". I want to ensure I know the procuations. I read on safety with these. Thank you!