I was looking for something that could fit four 18650 cells, when I found a holder that takes six. It's actually a holder for 10 R6 but if you take all plastic "walls" and battery connectors away the six 18650 cells fits perfect! It won't get much more compact!
I will post more pictures when I have done some soldering.
Mtbr's 2016 Winter Biking GearReviews and Roundups
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