Di2 booster - Any ideas?
 

Twice now I have run the Di2 battery down and both times was a long way from home. Yes, I was careless, but it happens.
So on my single speed ride back yesterday I had this thought...why couldn't you have a battery back-up that you plug into the charging port that would supply enough juice to operate both shifters until you got to your destination? Same idea as what people use for phones.
Anyone know where to obtain the "rare" Di2 plug? Yes, I could buy an external DI2 battery, but they're a bit expensive and a bit heavy, and you would need to pull the round E-tube connector rather than the charging port connector. It seems like a 7.4V battery of low capacity shouldn't be that hard to find.

One could hypothetically do just that. I know there was a story about an individual that charged their Di2 system on an Alfine bike using the Dynamo hub and a Dynamo-->USB converter. I don't think you can go straight from the battery pack to the di2 port however.

With a large enough battery pack (or one with enough Amps of flow), one could go from battery pack, to the Shimano charger, to the charging port. (Micro-usb input to Di2 plug on the output) I would guess that the SM-BCR2 has some circuitry to prevent power from flowing the wrong direction.

https://media.performancebike.com/im...ut-quality=100

just wait a little bit, you'll get what you're after...

https://www.bikeradar.com/us/road/ge...rge-di2-51334/

What would happen if you plugged a second di2 battery into the system?

The Di2 indicator light turns red at about 25% charge no?

The only fix needed is just better maintenance of the bike imo.

Or go eTap and carry a couple spares.

What if you forget to recharge the back up, too?

See my revised OP.

Yes/no, it locks you out of the big ring and you have presumably 100 shifts left. Not bad in flat country!
And yes, better maintenance, but the battery life is so long, you forget that there's even a battery there! ;)

LOL, there's that!

BTW I did find out that the 7.4V is quite common, in fact I have one in my Nikon D-90.

I feel like this was a post that was jokingly prophecized.
When Di2 was first announced, there was that guy,
"Can't wait for the first post asking about dead Di2 batteries"
No, others said, you'll only charge it twice per year, it is a non-issue.

The future has arrived.

Shimano already has a self contained system for those that can't be bothered to charge every few months

that pulley dynamo is cool though. Never have to plug in again.

The Di2 battery is 7.2 volts. That's not a common power pack voltage. Is it really that hard to charge your bike three times a year?

Charge on the 1st of every month, whether you need it or not.

Interesting post - yesterday went out riding with a friend who (stupidly) had not charged his battery. We came back to the house and picked up my Shimano cord/charger and connected it to a lipstick battery. We were able to ride and he had full use of his rear derailer - did not get charged enough to use the front one though.

btw,
to check battery level is super easy- just do it at the coffee stop or anytime:

push and hold left lever for half a sec (front mech small ring)


100% remaining: Illuminates green (for 2 seconds)
50% remaining: Flashes green (5 times)
25% remaining: Illuminates red (for 2 seconds)
0% remaining: Flashes red (5 times)

Correction - 0% remaining : NO FLASHES :bike:

Thanks all, Evidently there is a chip in the charger that communicates with a chip in the battery to allow passage of current. So a "battery back-up" is officially a "no-go" at this point.