USB batteries

[Maximilian Hohmann]

Hello,

just a quick report about using "USB batteries" in vintage HP calculators. Some time ago I was given an assortment of these batteries by my son who saw them in a museum shop. Now they can be found almost everywhere at very interesting prices (like on Amazon, eBay or Aliexpress. I don't provide links because these tend to be very shortlived). I have seen them in sizes AA, AAA and 9V block and they have the exact same voltage of the originals, but inside they contain a rechargeable lithium cell and some electronics. They have a small USB socket are are recharged from any 5V USB supply through a standard cable.

So far I have tried them in woodstocks, classics and an HP-71B and they work just fine. I have had a couple inside a 29C for over three months now and there is no noticeable self-discharge. I don't know what will happen if one connects a device contiaining these cells to a charger because they are not supposed to be charged through their normal connectors, but I guess that they have some sort of protection.

As far as I am concernded I will never buy a disposable battery ever again.

Regards
Max