[General Accessories] xaccers:
Please do not listen to MuF123 you may damage your phone.

Firstly, what people call voltage is actually Potential Difference (volt is the SI unit that PD is measured in), but to keep things simple I will use voltage.

To put things basically, when you are charging a battery, you are flowing current forcefully backwards into it, which is acheived by applying a voltage which is greater than the rating of your battery, hence why your car's battery is 12v, but the alternator produces 14v, and why a phone battery is 3.7v but the charger outputs 5v.

Picture your battery as one end of a seesaw, and the charger as the other. The current is a load of marbles on the seesaw. In proper use, the charger end is higher (5v), and you can imagine the marbles rolling down to the battery end.

Now imagine you used a 3v charger. The minimum safe voltage of your battery is approx 3v, although for safety your phone will switch off just above this to prevent damage to the battery. So picture your see saw with a 3.2v battery at one end and a 3v charger at the other, and the marbles will roll from the battery to the charger, discharging the battery down to 3v potentially damaging it and definitely never charging it above 3v so it will never be usable.

See the danger?

Now, charging a battery, or using any electrical device isn't just about the volts, it's about the current too (amps).

People often mistake the current as something which is pushed rather than something which flows, so they look at the charger, see 1A, and think that it WILL push 1A through the wires. It doesn't work like that. An electrical device will draw as much current as it's internal resistance allows (remember I=V/R from physics at school?).

This means you have to make sure the power supply can provide that amount. It's how fuses work. A fuse will only allow up to it's rated current flow through it, if you try to draw more current the fuse gets hot due to it's internal resistance and melts.

Now, remember the fuse. Also remember that the charging part of the charger is actually inside the phone, the thing you plug into the wall just provides power.

If the charger inside the phone starts drawing more current than the powersupply can provide, it will act like a fuse and get hot. Unfortunately when it blows, it's likely to catch fire.

Thankfully the charging circuit inside phones are good at preventing this from happening.

So what current output should you go for? Well, if the phone is going to charge when it's switched off, then a low output one will do, it will take a while to finish charging though.

You see, you have to provide not only a higher voltage than the battery to charge it, but also be able to provide a higher current than the phone itself is using.

For instance, say your phone is using 500mA browsing the web via wifi, and you've got it connected to a 300mA power supply, then it's not going to charge, the battery is having to provide 200mA.

This is why many new phones are being provided with 1A power supplies.

As I said, the phone's charging circuit is intelligent and tries to negotate with the power supply to find out what current to draw.

I believe if no negotation can be made, then only 100-150mA are drawn as a safety measure.

From the sounds of your kernal it can negotate/control the charge, in which case, as you are charging over night, I presume with the phone on standby (phone on but screen off) then a low charge rate will help the life of your battery.

For example say there is 1A power supply, and on standby your phone uses 5mA, so that's 995mA going through the battery to charge it, which can produce a fair bit of heat and help shorten your battery's life by a little bit compared to say only charging at 100mA, assuming you're charging both from nearly discharged.

Top up charges are better for lithium batteries though as they're short so while the higher current will be flowing, it won't be for long periods.