On long GPS guided rides I've had a problem with my phone; being that when it's plugged in, it gives a message along the lines of "You're not charging me enough son". Ultimately leading to a flat phone battery and guessing the way home. No longer I say! I've found that (on android at least) unless your USB charger has the D+ and D- pins connected then your phone will only charge at a rate as if it were connected to your PC (~50%), not the full tickle it would get from your proper manufacturer's AC charger. Being too cheap to fork out for a couple of new chargers and too lazy to split the ones I have in half to solder the connectors up, I've merely put a tiny bit of aluminium tape over the middle two pins of the USB lead and I now have full charging capacity! Check it out yourself - plug your phone in and look at the battery level - it'll say "Charging (USB)" or something. Then use a doctored up lead and it'll say "Charging (AC)". Obviously, don't do this on your computer lead as you'll not be able to transfer data.