Which Groupset?

How often do you need to charge Di2, and how do you charge an internal battery? A long USB cable or?

Not trolling I just don't know.

Shimano said about a thousand miles depend on how much you use it, annoying thing about Di2 is that they don't sleep (unlike eTap).

You plug a USB in to the junction box under the stem. It takes about 45 minutes.

About 60 hours is what I've found.

USB cable into the junction box at the stem.

I've never run it down - reviews say at least twice as long as eTap 2500k+

I charge it before big races.

Have you done any big races?

Eh? Why would they need to sleep? They don't use power when they're not moving.

I'm sure I read that eTap doesn't sleep and some teams were keeping cabled bikes as spare bikes for that reason.

Every race I'm in is big.

Di2 supposely have a sleep mode, but I don't think it work as well as they said, as the battery drain after months of inactivity.

I'm gonna look into this more, eTap sleep when not in motion (not useful if you want to move it).

How does one wake their eTap?

Big kiss and a cup of coffee?

Talk gently to it.

In all seriousness, it got an accelerometers.

From Bikeradar so it must be true:

1. It falls asleep
   
   

If you sneak up on an unsuspecting eTap group and ever so gently touch a shifter without moving the bike in the slightest, nothing happens. The group is sleeping. Accelerometers in the derailleurs wake the group at the slightest movement and keep it awake for a time even when still. When you are riding, it’s always awake.

This auto-pause feature allows for a longer life (a claimed 60 hours or 1,000km) with the 24g battery.

Do you have D-fly?

I definitely dont charge mine that often. Thats like 20 rides!
I reckon I get more like 150 hours

Which makes me forgetfull. Which isnt helped by my Junction A being hidden.

PS I should now out myself as an eTap user. I have never successfully sneaked up on it and pushed the leaver without waking up the derailleurs. Makes me think there's a sort of 'does a tree falling in the woods with no one to hear it'-type scenario whereby the only way I can prove the alleged accelerometers actually exist is to change gear without touching the bike. Or even being in the same room. It's Schrodinger's Groupset.

https://seasonalcommute.com/2015/02/16/di2-battery-life/

"Two, the current draw while off is small enough relative to the other loads that it can be ignored. With these numbers the system could sit for over three years before the battery is discharged."

"Moreover, the default mode for the shifters and derailleurs is 'sleep'. A button push instantly 'wakes up' each shifter's transmitter, and that signal correspondingly activates the uniquely paired receiver.

SRAM's patent documentation doesn't outline specifics in terms of run time but it does claim a power draw that's just one-tenth of a wireless system that's always on. The automatic sleep mode means users won't have to manually shut things down, either, as is required for Campagnolo EPS."

'instantly' wakes up.... hmmm... I'm thinking reboot and chkdsk scenarios already

https://www.youtube.com/watch?v=iHW1ho8L7V8

in 1 eds

"SRAM has acknowledged this slow shift speed, saying that the decision was made to slow down the shifting speed in an effort to prolong battery life"

It wasn't in an article, it was in a comment:
"You forgot to mention that eTap stays on & suffers battery drain when being transported on a vehicle roof rack unless you remove the batteries. This is why some SRAM teams have mechanical Red bikes as spares. I also question how water resistent the battery seal will be after a year of the batteries being taken on and off. SRAM also do not actually state that its waterproof only that its been tested in wet weather."
which linked to:
https://sramroadsupport.zendesk.com/hc/en-us/articles/207514077-Will-the-parts-stay-on-when-the-bike-is-on-my-car-rack-

Di2 runs on CAN bus, so is most likely a really dumb microcontroller in a low power state waiting to be brought out of it if an input (attached to the shift lever) changes. If it does, it sends the CAN message to the derailleur and it's done.
Edit: CAN bus is the main comms protocol used in cars in case anyone's interested

Godfeckingdammit, all those hours I've wasted trying to sneak up on it and push the button without waking it up. Someone shall pay. So it's asleep unless you either push a button or make the slightest movement; it's not a very sound sleeper then.

What SRAM need to do is make a dummy battery to cover the derailleur to prevent exposure to the environment.