iPhone tethering. 3G, heat, and battery drain

I have an iPhone 3G and have been using the tethering feature heavily over the past month while travelling. In the 20 months of ownership prior to this period I didn't use the tethering feature for more than an hour at a time so a few peculiarities which exist never occurred to me.

Firstly, while tethering my Macbook Pro (2010 model) does not provide enough power to tether via 3G and keep the battery up. Whether the laptop is plugged into the mains or not does not matter, the battery will drain slowly. Secondly, If I turn off 3G the battery will not drain and will slowly charge while tethered.

Most importantly though, if you are tethering and the ambient temperature is high, the iPhone battery will not allow any further charging to come in at all which will run down the battery very quickly with 3G on or off. It's best to keep an eye on the battery while tethering to make sure you don't end up with a completely empty battery.

Bandwidth heavy applications will run down the battery faster as well since more more data is being transferred.

Running on laptop battery power:

47% at 7:14PM
49% at 7:22PM
53% at 7:37PM
61% at 8:29PM
65% at 8:47PM, turned on 3G
55% at 9:17PM
39% at 10:06PM
28% at 10:28PM, turned off 3G
40% at 11:00PM
99% at 12:53AM, turned on 3G