Di2 reliability is a closed issue and has been for quite some time.

J.

I fully understand why some are hesitant to trust electronic shifting. Without the experience I and the others I ride with have had I would too to some extent. Everything else i own that has a battery from phones to flashlights are somewhat futzy. I now have over 25K on a di2 that has lived on 2 frames and it has shown 0.0% futzy-ness. Original external battery was changed to an internal battery soon after I built the drive train and it shows no signs of failure. I charge it up every month or so. 10 min charge before a ride will give you a few days worth of shifts should you forget. Battery is a lipo and a fully baked in technology so I bet batteries will only become better over time. 2X rides a day year round. Only parts I have changed are wear items like chains and cogs. Considering that I have been able to upgrade the software the system works better than when new. The brifters are not complex cable spools with ratchets and release mechanisms with little parts pivots and springs. They are simple sealed switches. In many ways electronic is less complex than mechanical. It offers all that mechanical can and far more. put shift buttons where you like, no ghost shifts under heavy load, and you can tune the speed and format of the shifts. Di2 crunches right through slush and ice up and down shifts while in the same conditions my "bad weather bike" a cable controlled CADDX freezes up and refuses to shift to the smaller cogs and ring. Front DR auto trims and the RD trim if needed after a wheel swap is a button push to engage and then up and down shift via the brifter until silent.
My experience is not alone. Other riders I ride with with Di2 have all had trouble free ownership. I installed my di2 in late 2011 and time will tell if the system is robust beyond now and if Shimano continues to support it. So far other than the original DA electronic with the bulky non can-bus wiring things are readily available with more things being added that are plug and play. Non conforming bikes can gain even greater value from electronic. Tandems and time trial bikes come to mind. As an example my old school steel downtube shift tandem has one real loooooong cable going the the RD and a nice mushy feeling RD to go along with it. Unlike a single you can't take a glance down to see what cog you are in but my Garmin edge shows me via the communication it has with the Di2 system. My next tandem will be di2.

Really ?. Just for giggles I checked on Jenson. Di2 external battery is $50. Internal is $100. An Ultegra 11 SPD chain is $22

Is my math wrong ?

Well your math isn't wrong unless you consider I've been running Di2 for over 2 years and it has functioned seamlessly including the internal battery. In that time I've gone through at least 3 chains so that would bring the price comparison closer into line. Since I am still on the original battery so who knows how many more chains would come into the equation.
Even at the price if I had to replace the battery I would just consider it an acceptable price of maintaining the system. I like it that much. Crisp shifts and almost maintenance free. I don't miss replacing the cables but that's another issue.

Well I happen to agree with you that Di2 maintanence is not only easy but not that expensive and possibly cheaper in the long run then mechanical, IF you do part replacements (chain and cassettes) that would be required of high mileage riders.

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.

That's what I thought but since you are the one that made the comparison I responded to it.
BTW I've had a crash with the Di2 and other than having to reset it from accident mode at the junction box it came through unscathed.

Lithium Ion batteries put out more power in smaller package but they suck for long use. The old NiCads would last for years but they couldn't get the battery small enough yet produce the kind of power they wanted. So you have to pay for the power and portability with more frequent battery replacements. This is why it's important when looking at a expensive light that the battery can be replaced when the time comes.

Nickle metal hydride batteries are just as bad, this is why when I bought a new drill a few years back I got a one with a lifetime warranty including the battery!