How to check the battery level of devices connected via Bluetooth in OS X I have a set of Bluetooth headphones that I use with my iPhone and Macbook (OS X Yosemite). 

On my iPhone, a little battery meter pops up next to the Bluetooth logo each time I'm connect the headphones.  I have found no such option on my Macbook (OS X ) and am wondering if anyone else has experienced the same issue.

The only potential solution I came across was the Battery Tracker on the Mac App Store. It is not clear whether it supports all Bluetooth devices (and not just standard peripherals), and I would rather not pay the $1.99 to find out.

I know that my headphones have the A2DP Bluetooth profile, so my gut is telling me that information about my battery level has to be accessible somewhere on my computer.

Here is a screenshot of the device profile from my mac's System Information. RSSI seems like the only thing that could have been a battery meter (everything else is booleans or id's), but from what I've read it seems to be a metric for signal strength.

I'm interested in finding a solution from a practical standpoint, but am equally as interested in understanding how it would be/is achieved from a technical standpoint.  Think I just need to figure out what the battery metric/param/variable is called, and where I can get it.

Please let me know if you have any thoughts/insights ! Thanks
I hate to have to answer in the negative but the answer is: you can't. 

I've done a lot of searching the web, testing utilities, playing with ioreg on the commandline, scrutinizing System Profile reports, and it appears to me that OS X has no way of displaying battery level of connected devices that don't automatically display battery status in their Bluetooth menu Device submenu, even if iOS devices display detailed level info for the same Bluetooth device when connected to them. OS X just appears to completely ignore this capability in all but a few default (Apple-manufactured, it appears to me) devices.