Unlike the PB100, the Portable has easy-to-rebuild batteries. Once you've opened it up (some minor cracking required), you'll find ordinary gel-cells inside. If you can find a source of new cells, it's easy to swap out the bad, swap in the new.

I had a stash of smaller gel cells, so that's what I put in. The battery life isn't as good as with the original, but still plenty good enough.