Sharp PC-1211, battery question

[isidroco]

From first comment here: https://www.tindie.com/products/halfbake...p-pc-1211/

"I'm using THREE silver oxide batteries to keep the voltage close to the original four mercury batteries. The fourth (left-most) battery apartment I've shorted by a flipped battery."

So there's no need to solder or change original circuit, just use an old (or new) battery upside down which will jumper that compartment.