I've been generally pleased with my Di2 setup since getting it installed almost 2 years ago. I have accidentally depleted the battery a couple of times to the point where I lost shifting on the front derailleur, but other than that I've never had any mechanical troubles with it.

Last night I had it just quit working altogether. Somehow I managed to drop the chain, but I don't know if it was the cause or the effect of the Di2 problem. I just barely wedged the chain between the small ring and the frame, but did not force it. When I got the chain back on the small ring the shifting on both the front and the rear didn't work at all. There was no green light on the indicator. I thought maybe it had gone into "crash mode", but I couldn't get it to respond even by holding the button on the indicator.

Finally I thought to remove and replace the battery, and it all started working again. I've never heard of anybody having this particular issue before. I'll run it by the mechanics at the bike shop next time I'm in. Hopefully it was just a one-time fluke.