They're a bit hit and miss. You have to use just the right size drill for the material, and half the time you have no idea what that'll be until you try and use them.
Plugs are just easier for most things.
Yeah, internal antennas (of the cheap, PCB printing type) are cheaper, also look 'neater'.. and don't work half as well.
I've used those along with several other models. Hardware-wise they work well. The stock firmware is pretty decent and will probably satisfy you. You can get an idea of the...
Internal antennas, not exactly a recommendation. Looks slightly better than the typical tat, though..
Try this: http://www.amazon.co.uk/TP-LINK-TL-WR841N-300Mbps-Wireless-Router/dp/B001FWYGJS
If you want something really decent you'll be spending a bit more than £30.
Batteries show a high voltage into no load after a charge. This voltage immediately vanishes under significant load, it does not relate to stored energy.
Under unloaded conditions you'll get a drill spinning faster. As soon as you load it down it becomes irrelevant.
Does it actually have a warranty void sticker in the way? If not, get on with opening it. If it does.. go get a bit of wax paper and get rid of the sticker, then get on with opening it.
It will not be as simple as a 'small plastic link' (what, exactly, do you expect plastic to do? It conducts worse than air!). It may be possible to change, or it may not. Nobody is going to be repairing these, though, so good luck finding someone who's opened one.
Feel free to open your own...
If the thing comes with a cable which lets you plug it into a USB port, it gets to deal with all the charging. The USB port, whether it's a host port or a charger, cannot act as a battery charger, it can only supply power.
Charging is a different matter. Many devices will happily use in excess of 1A if told they can.
http://www.usb.org/developers/docs/usb20_docs/usb_20_031815.zip
Or better, send them to an independent laboratory to be tested according to the regulations supposedly enforced in this country. And send the gigantic fail reports far and wide.