If you've ever wondered why cellphones don't work without a battery present at all, even when plugged in, it's because they're used as a capacitor effectively for the cellphone radio. The peak currents of those can exceed several amps momentarily so you need to have quite a lot of power on hand (even exceeding the charger) for times when you want to transmit. The amount of total energy being used from the cell is close to nothing however.
I'm surprised yours works at all, it must be fairly marginal.
All I can say is that it isn't an uncommon operation to do.
I have stress-tested it a bit and know that it won't be a problem for me, certainly not for the music and navigation I will be using it for. Also as far as radios go only wifi+bluetooth.
I'm surprised yours works at all, it must be fairly marginal.