I've bought a LED head light some time ago. Battery turned to be absolutely useless. It runs only 15 minutes instead of 12 hours. It has two holes inside, but there’s no liquid. Maybe all went off, and thus there’s no power… Even if had something, I don’t know what to put there, acid, alkali, water?..

Anyway, I got USB cable, soldered it in place of battery and 220 AC charger board. While I have PC I can use USB. Otherwise I use my bullet-proof Ericsson R520m with USB-to-serial cable, which I’ve upgraded to provide power to the phone (white wire). Both cables are connected via double USB A connector (from a mother board).

Thus, head-light works fine anywhere :).
http://like.by/ftp/led.jpg (upload seems to be broken)