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After doing nothing about it for years, I finally replaced the battery in my HP75C.

I ended up getting one of those cordless phone NiCds which was shrink wrapped in white plastic and contains 3 AA batteries.

I cut the plug off the wires and soldered them to the gold contacts. I noted the battery website which explained the polarities. I also connected the extra tab to the black wire which I think charges the battery. (I still have the charger).

The main problem apart from being rusty in soldering, was that I couldn't get the battery cover back on.

Eventally I slit the shrink wrap because the original battery had deep grooves for the gold contacts (and some blobs of solder) which were not now recessed on the new battery because of the shrink wrap.

I also had to shave some of the ribs inside the cover as they were stopping the cover from sliding on.

Now it's all working except the battery came fully charged and I now have to wait for it to discharge before I charge it. I will also remove the cover when charging so I can check the battery temperature in case I wired it up wrong.

I don't think so because the charging tab lined up with the negative groove on the battery.


If you wired the battery incorrectly, then your 75C would not work.

Not to mention that it is a bit too late to wonder about whether you have wired the battery correctly after you have installed it in you classic computer.