Press and hold any of your shifting buttons for at least half a second. The colour and the amount of flashes of the junction box LED indicates how much charge is left.
Of course the LEDs cannot flash if the battery is completely empty, which is why a more accurate approximation would be:
- Green for two seconds: more than 75%
- Green, flashing 5 times: 50% – 75%
- Red for 2 seconds: 25% – 50%
- Red, flashing 5 times: less than 25%
Please note that when you have 10% or less charge remaining, the front shifting will cease to function. You’ll be stuck in the chainring you selected.
Depending on your firmware version, it’ll also display flashing lights to indicate the shifting mode you’re in.