This is a great idea. I'll dig into this more.

The battery profile is a GATT profile, not classic; so this would really only work with dual mode devices.

Thanks rkc@ but it seems that even for dual mode devices we don't currently support the battery profile. 

That is correct. Not enough prevalence of dual mode devices for it to have been worth it. As we do see them uptick, we could up this feature in priority.

@RKC, would it be possible to revisit this now?

With the Bluetooth 4.0 specification effectively imposing dual mode support, the growing prevalence of Bluetooth 4.0+ devices in general, and upcoming Fast Pair support, I think now would be a great time to prioritize this FR.

If we move forward, ideally the battery percentage would be included as part of both the Bluetooth sub-menu within Quick Settings ("Connected, Battery: XX%") and Chrome OS Settings > Bluetooth (same format).

James now owns connectivity in Chrome OS UI, over to him.