any i have opened were held together with screws
if there are on screws it may be a sealed unit not designed to be re-opened
the batteries in side will all be spot welded together with metal strips so you would need to break the batteries apart
a 12v pack will probably have 10 1.2v sub-c size cells at least that's what was in any i have cannibalised so if you want the batteries you will not be able to use it for your power-tool again if you need it for your power-tool don't take it apart
Is it the stick type or the block type like most other power tools. The long stick type the end opposite the contacts comes off, there are two tabs on the sides you push in to release it.