I’ve been running Di2 since 2015, in that time I’ve had 3 issues
1st, at 2AM I took a tumble down some concrete steps at Gatwick en route to Brighton on a FNRttC. (April 2015) We collectively spent 45 mins trying to fix the issue including a lot of helpful googling for crash protection etc. The issue turned out to be the right shifter having taken a whack and rotated on the bar had pulled out the cable, once reconnected I was back on my way.
2nd issue was a pure mechanical one (2015 again), a chain quick link was far too worn to be in service and decided it wanted to depart. The side plate snapped resulting in the jagged remains jamming in to the jockey wheel with the inevitable RD being dragged in to the spokes and destroyed. Luckily this was on the way to the train station from home (on another FNRttC) so I was able to get home. The parallelogram on Di2 RD is made of cheese so a new RD was required.
Final issue was earlier this week, the battery on a bike went from 100% to 50% in 30 km. Quite alarming as I’m planning a 400km perm this week. My current theory is that it might not have been at 100% in the first place – suspect the laptop it was charging off might have gone to sleep before it was fully charged. I confirmed it was at 100% last night and it is still at 100% this morning, so keeping an eye on it….
In terms of waterproofness – well I’d say it worked pretty well through the jet wash conditions of Yadd Moss on LEL last year. Here’s a fairly accurate ACME simulation (but with less water than we had!)
https://twitter.com/ACME_Essex/status/911531999244013568You get plenty of warning of low battery, helped even more if you have the ANT+/BT connection running and can see the battery charge on a Garmin or similar head unit (charge is shown in steps of 10 from 10 to 100%) or if you have the BT unit, you can also use an app on the phone. On low battery, the FD stops working and there’s probably ‘a good chunk’ of shifts remaining on the RD. I have never got myself in to that position from memory (though might have had it once in 2015?)
I charged the system once on LEL sometime after St Ives (I think) as a precaution (I think it might have been down to 30%?)
In terms of on ride bodges – as Kim has pointed out – they missed a trick having some sort of physical position adjust in the event of lockout. I’ve never had the crash protection kick in so no idea on what the RD does when that happens other than it stops working!
If it all stops, you are still left in some gear – just it might not be the one you need. 2 alternatives there, one, stay in that gear and work at it….
Or more drastic would be to drop some links out of the chain, bypass the RD and select a desired gear. The latter being no different to if a mechanical RD snapped off of which I have seen lots of times on other’s bikes…. Only drawback here would be if you are running oval chainrings this option might not work.
All these systems have their pros / cons to weigh up when deciding what's right and I can't remember the last time I saw a thread entitled "In praise of $type gear shifting system"