External Battery/Replacement for Clip+

I’ve got a collection of Clip+ players that I’m hoping to keep going, since I can’t seem to find anything comparable.

I use them mainly for podcasts, and the feature I depend on is that that the navigation ignores empty subfolders. I can’t find another model, either from SanDisk or anyone else, that has this.

So, two questions:

  1. Is anyone aware of an mp3 player that does this ignore-empty-subfolders feature?
  2. My oldest unit is about 13 years old, and amazingly it still works, tho the battery only holds for 4 hours, and I just bought a “new” unopened one whose battery works for only 100 minutes. I’d be happy to use a player with an external battery with a USB output if I could find one small enough. So is there a tiny cell phone battery, with say only 500 MaH (the player’s is only 290 MaH, as I recall) that anyone has found that works for this purpose? Even the smallest cell-phone external batteries seem too clunky for purpose.