The battery is by far the number one di2 part that gets replaced by Shimano (under warranty).
I know. But you don't understand how hippyluck calculations work. If I'm thinking about Di2 spares and decide not to carry any, there is 1000x more chance of Di2 failing...
I wonder why new batteries are an issue. Maybe straight from the factory with a poor cell not holding enough charge? Once it's fitted and working I don't see how you can ruin a battery such that it won't charge (I'll find a way now).
The battery is by far the number one di2 part that gets replaced by Shimano (under warranty).
LOL