Advertising Battery levels on a beacon

Hey folks,

I am currently trying to use my nrf51822 evaluation board as a beacon. This is working pretty well but I need to have it broadcast its current battery level as well. From what I have seen this means I need to make some kind of interrupt to tell the chip to update the advertising message. Could anyone point me in the direction of some information on this topic?

If it helps I am currently basing everything off of the ble_app_beacon example code and that works just fine.