I have an old (very old!) style (green) Ozito 18v lithium ion drill. One of the two battery packs died some time ago but I have survived with using the second one until it too has just died. It appears to charge but runs out of puff after a very short time. After charging it's reading over 20v. I'm assuming it's the battery and not the charger. 1 - is that a reasonable assumption and how can I test? 2 - if it's the battery pack, then how can I test if it's the BMS or the batteries? 3 - If it's not the batteries, can I deconstruct both packs to get one working unit? 4 - if it's the batteries, is it best to simply buy a new unit (not sure if they are still available) or buy some new batteries to install in the unit. 5 - if the latter, then what do I need to look out for? Lots of questions! Any advice welcome. Thanks.