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My HP-28S still works after 30 years. The battery door is missing a corner but it still works!

I didn't know this was a common problem.

These days I mostly use PCALC on my iPhone. I like the ability to customize the number displayed lines from 4 up to 8. There's free version too : PCALC Lite

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It's a very common problem. If you google "hp 28s battery door" you find a lot of discussion.

At one point somebody made a metal band that goes across the back of the calculator and holds the batteries in. They don't seem to be available anymore, but that's basically what I need because my battery door is in decent shape, but the case is cracking at the corners.

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