@typhlosion that was the norm for the longest time, many IBM PC-compatibles as well as early Macs had these terrible rechargeable lithium batteries (not the same chemistry as modern li-ion i don't think) for holding the cmos memory, and they would eventually leak after years in storage and the corrosive electrolyte wreaks havoc on the motherboard they're soldered onto
countless old computers have succumbed to the cmos plague
-F