Originally Posted by rm -rf

Lithium batteries don't need to be drained toward empty. I only check my battery charge occasionally, and charge it soon after it goes from solid green to blinking green. That's at the 50% charge level. I've only twice forgotten to check often enough to get where the front quits shifting. (I usually think to check while I'm riding--that works easily, it's just holding down the front shift button for 5 seconds.)

An old 1.3A phone wall charger works fine. I just keep it connected to the Di2 charge cable--very convenient.