....... and if you don't mind a challenge -
Take the battery pack apart. You may have to prise open the plastic case, they often have no screws to avoid people meddling!
If you can open the case you should be able to access the original cell/s.
You have the electrical rating, and you can now measure the physical size of the cells.
With all that info try Eurobatteries website and scroll through the huge list (illustrated) for a match.
If you can find a match all you have left to do is solder the new into the pack and re-seal the case with whatever seems appropriate.
I have succeeded with replacing batteries in a cordless drill, an ancient mobile phone and a normal cordless phone.