In my case, makita's original battery (NiCd) didn't have any BMS (Battery Management System) whatsoever, but lidl x20v system batteries do have integrated BMS in the battery itself, so that protects you from any over-charging and over-discharging. So, any older, especially NiCd generation tool is ideal for conversion. I had some tools bought that had some sort of primitive BMS in the tool itself, but i'd just scrap it and connect directly to battery adapter terminals, letting battery do the regulation. I'm yet to burn out a motor in a tool, or kill a battery, never happened. Plus, x20v batteries are quite smart when it comes to over-current - if i stall the drill/saw, battery cuts off completely, for a short time, then i release the trigger for some time (~5sec) and battery re-enables the juice flow. Smart... Bit of a draw back, but if i'm being an eejit stalling stuff i'd rather have my tool not on fire and stall/quit temporarily...
I do RC stuff as a hobby, deal with unregulated LiPo batteries all the time and know what happens if you mess with that too much - hiss/boom/FIRE... (yep, i did destroy batteries in the air (over-discharge), disposed of batteries in fun way by piercing them while fully charged (fireworks
) )... So, BMS regulated batteries dont really scare me anymore. I have a battery bunker/storage/charging station made of hollow cinder blocks, where i keep all my LiPo and tool batteries when not in use...