Probably the most convenient place for the clock battery : r/ps2
Amazon.com: OLD SKOOL EXTENDED 3.6V 3600mAh Li-ion Rechargeable BATTERY PACK For SONY PSP 1000 (Fat) : Video Games
Your phone battery isn't fat, it's just dangerously swollen | TechRadar
Duracell Coppertop Alkaline Batteries, D D | Walgreens
Electric Bicycle Ebike Mountain Bike, 26 Inch Fat Tire Electric Bicycle with 48 V 18 Ah/Lithium Battery and Shimano 21 Speed (Ersatzbatterie) : Amazon.de: Sport & Freizeit
COMPATIBLE BATTERY FOR PSP 1000 1004 FAT GORDA 1800 mAh BATTERY 1001 1002 1003