Some customers ask me why we do not refurbish and repair akku packs for the HP41c family (you know, these packs that were charged through the side hole in the calculator). The reason is that there is a cheaper, more logical solution: the rechargeable N-batteries.
These can be found in Amazon:
You can also find the charger in the same page.
I have found also other rechargeable n-type batteries in Amazon, but I have not tested them. I have bought the Odec and can attest they work fine with the recharger provided, so this is what I recommend!