I think that the battery should be BLUE, red is in A4000, IIRC.
its near the 68000 CPU (loong chip), relatively close to mouse/joy ports. I had one a2000 that had very bad batt. leaking (and corrosion), its CPU had green legs. Once that green (oxide?) stuff was removed from 68k legs, A2k worked :banana: . If you haven't change anything since it worked, its gotta be the battery.
BTW, you can even disconnect FDD (together with all cards like melott told you), but then wait a bit longer for KS(1.3?) image to appear.
Most important would be to see some change from black to anything else (grey and white preferred) :-)
PS. I prefer litiumhack to phone batteries (check older posts)