Good point from another website:
And to the OP, no, when a phone is off, it will not ping the cell towers. That would kill your battery in short time. Could you imagine the complaints it would generate from people who turn their phones off frequently? Turn your phone off when it has a full charge, and it's down 30% when you turn it back on 12 hours later?
Well that's not necessarily true - That supposes a frequent ping. Lets suppose in theory that the phone is only pinging to maintain the lease... As a feature, btw, to ensure a quick boot time (
) ... That would be a ping, what, every 12 hrs or so? Which would hardly effect battery life.
So it would matter how often the ping occurs. How often it is, I don't know.
I can tell you the phone will go dead eventually even if shut off. I have often left the phone in the truck*, walking off, and returning days later, the phone has lost significant battery.
*The phone is useless beyond cell range.