Internal or external DI2 battery

[rodriguo]

Hi Dave,

I have read your blog since I'm doing something similar. I bought the shimano Di2 6870 with the external battery mount and I will like to replace the battery (SM-BTR1) by another voltage source but I'm not sure about the polarity since there are three contacts. I know the battery rated voltage is 7.2 V but I have tried to power the system with a voltage source using the two big contacts that can be seen on the external battery mount but it doesn't work, so, I guess I should do something with the third contact.

http://cdn.carltonbale.com/wp-content/u ... _Mount.jpg

Hope you have the answer.

Thanks in advance,

Ricardo.