HP-12C+ show Error 9

[grsbanks]

(06-21-2018 09:56 AM)Gamo Wrote:  I checked the batteries both are good with a little bit above 3 Volt on both batteries.

If that's the voltage across the batteries when there's no load on them, it means squat.

As batteries age and run down, their internal resistance climbs. This means that the voltage across them dwindles for the same current being drawn from them.

I think HP usually put Maxell batteries in their machines and they're OK. What you don't know is how long those ones have been hanging around and how long they've been in your 12C. They're not expensive so don't waste any time thinking about the pros and cons, just replace them. With well-known branded batteries.