Originally Posted by Isoprop
As you have found out, unlike the #16, you can't use USB power without the internal battery connected. However, you should beware of using 5V applied directly to the battery. It will work, but the question is for how long. You are definitely stressing the components. Maybe you should consider putting a small diode in series with the positive lead. This will reduce the voltage to a safer level and as a side effect you will benefit from reverse voltage protection.
I received a #11 from a user which had been very badly damaged by supplying over voltage. Even the DRAM chip was destroyed.
I don't have any diodes lying around but I do have some small resistors and was thinking about experimenting with them? Reverse polarity protection isn't an issue as I'm using a polarised plug/socket in the flylead.