They take camera batteries. Here is a list of replacement models: http://mypage.intergate.ca/~fspencer/8580prob.htm

Years ago I snagged a bunch (new in their individual packaging) for next to nothing on ebay, which was good because after that I started getting a flood of PS/2 machines).

Reference disk is here: http://ps-2.kev009.com:8081/pccbbs/refdisks/rf7080a.exe