Just picked up a fleabay special. Battery has some juice, but not sure how much. Have cycled it through the settings a few times but not left it on for long. What should I do next: run battery until drained or fully charge it?

Just charge it, Li-ion batteries don’t like being run all the way down (IIRC correctly..)

Depends if you’re planning on using it, LiIon don’t like being stored fully charged either. If it’s getting ready for winter then just leave it part charged.

^^ that is very true.. bloody li-ion batteries!

Keep them in the fridge at 40-50% charge when you’re not using them for a long time.

If you want a reliable battery pack, get one of those cases that take 4 batteries, that way you can buy and use quality batteries, and them take them out and charge them separately which is safer.
Or, you could contact Smudge (mtb batteries) and see what he has on offer.