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Thats the neat part, its right there at the end of the handlebar, just click the button and its on. Can be done on the go. Battery drains dead in 3 days, and its not the one bike I always use so itd be hard to keep track of always making sure its charged before I ride. Id much rather reduce it by remembering /most of the times/ to disconnect the left shifter with the bar-end button.
I also hate binning otherwise fully functional stuff, and spending money on replacing them. Hack/bodge is the way for me :)
and remember after every ride to turn it off. And turn it on again at the beginning of every ride. For me, at least, the former would be the hard bit of the plan.