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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

I have been using these for a few years and agree they work very well. I did some limited capacity testing to compare them to good quality alkaline batteries. The short story is they have about 75% of the capacity of an alkaline cell. The link to the video I did on this is below.

These cells tend to have two types: 1) Have micro-USB connector on side of cell, 2) No connector. I prefer the second type which are charged by placing 5V across the cell. The build in charge controller takes care of things. The downside is that you need a little 'dock' to plug the batteries into. The dock plugs into a 'USB' power source.

https://youtu.be/hzYknX2GFBU

I've also been using these for a while in Psion Organisers. They work well, and you can pop them out and recharge very easily, no need for a special charger, just a USB able and some power source. The Psion uses the PP3 9V type.
I've also got some AA sized versions that I use. The only downside I can see with these batteries is the cost...

Hi Max, thank you for your report, did you know if are also available "USB batteries" for the 41's?

Thanks for the positive comments everyone, especially Max for opening the conversation. I've been wondering about these myself and it's good to know they are another safe option. I now use mostly Eneloops and a few Alkalines, but also would like to stop polluting the country will dead alkaline cells, so I can shift to a few of these over time.

(08-08-2023 04:46 PM)rprosperi Wrote: [ -> ]Thanks for the positive comments everyone, especially Max for opening the conversation. I've been wondering about these myself and it's good to know they are another safe option. I now use mostly Eneloops and a few Alkalines, but also would like to stop polluting the country will dead alkaline cells, so I can shift to a few of these over time.

Hi Bob, I've been a little away and Jumped today back to the Forum, so just now I'm aware to have missed this previous Thread and the old post chained. Do you mean these eneloops? they are not available unfortunately in N-size, I think
Hope Diego's project soon will be completed

My dad gave me 4 of this style and I have made use of them in several places. They're convenient for recharging anywhere with a common USB A port available.