>If you do > 500km riding a year it's a worthwhile upgrade IMO.

Did you miss a zero? I do 500km a year, taking my kids to nursery on my beat-up old MTB.

Probably. I did more than 20Mm (20k km) so far on my mechanical 105 in 2 years and had to replace a single rear shifter cable in between. Mechanical transmissions are not exactly high maintainance either, and maintaince is fairly trivial. Probably would have spent more time charging batteries in 2 years with DI2 than with cable fixes and adjustments on mechanical. But I'm still somewhat intrigued to try it.

I love biking because it makes me independent. Adding electronic complexity and the need to charge is the antithesis of why I own bikes.

I might have to change the cable once in a while, but I don't ever have to upgrade the firmware.

Is there Di2 for MTBs? I'd like to get a new bike this year, but they all seem to be SRAM.

The battery need to be replaced at which interval?