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Biggest concern is the port in those batteries, if all the batteries have those micro USB port, then there's risk of water getting in from that and make the system go loopy (think of those rechargable light that often gone wonky when water is directed at it without mudguard, Moon Comet for example).
If however, those little black bit are removable battery and can be charged like a cochlear aid batteries, that would be a much better system.
Very much looking forward to full wireless shifting. Means it will be compatible with almost all frames, including older 90s/00s frames.