Originally Posted by Steve B.

........Of course you are changing a chain and cassette regardless if it's Di2 or mechanical, so kind of a weird comparison.

I only took umbrage at your comment that a battery is cheaper then a chain, as it's clearly not.

That said, I think the longer term experience of Di2 is it's going to be terrific in terms of reliability, even if you have to replace a battery every 3-5 years. Replacing things that might get damaged - derailers, shifters, is a different story as those Di2 parts might run 3 times what a mechanical part will run. Still, I've had 3 mild crashes on my 10spd. Ultegra stuff and while suffering some surface scrapes, everything works 10 years later.