Any tips?
Here's one:
I guess we can all give a hand to end in behalf of all of us, isn't it?
I feel strange that there is no mention of this:
http://www.tearlachwales.com/batbox4k
Using 4 x 18650 for 2.5 hours which is about 20 USD for 2.5 hours. Probably the minimalist solution have seen so far and it works wonder.
Tea is a great guy to deal with and I would recommend his service.