Wall Chargers

So I happened to borrow my friend's wall charger to charge my phone. I noticed that their charger was less than half the amp output than mine. It was pretty useless because the phone took forever to charge about 5%. I only used the charger for about a few hours. Could of this been bad for my battery?

it is only bad for the battery as it isn't charging it... It is bad for the charger as it can burn it out by trying to draw more current than the charger can put out... I am going to have to guess that the charger was kinda warm when you unplugged it... If you have a usb cable for your phone try plugging it in to your pc and charge it from there. (Thinking about the slow charging you did... I have never heard of a battery being hurt from slow charging, only fast charging. Fast charging requires a higher voltage than the battery nominal and thus a higher current gets pushed backwards through the battery causing more heat and wear on the battery)

"It is bad for the charger as it can burn it out by trying to draw more current than the charger can put out..."

In which case the design of the charger is pathetic, chargers should have over current protection where they will just shut off. This comes from one of the last devices in the chargers which is the voltage regulator. If the phone is charging to much current the regulator should shut off.

And if the regulator does limit the current, and it doesn't just one shot, it would cycle the charger on and off. This would still cause the charger to overheat and possibly burn out. That is why when you replace a charger you replace it with one with the same or greater current capacity. By definition the charger is not designed to be ran at greater than its rated capacity.

and also... why should the manufacturer have to put in safeguards such as overcurrent protection to protect the consumer from themselves? There is a current rating on the power supply for a reason. It is not their job to make sure that you use the correct charger for your specific device. That is part of standardizing the plug... If everyone uses the mini / micro usb connector. Standard USB 2.0 current limit for a device is 500 mA. If your device draws more than the standard it is not the manufacturer of the chargers fault, nor is it their job to foresee this. It is your job to get the proper charger for your needs and not to pass the buck to the charger manufacturer if you purchase the wrong one and it damages the charger or your device. They put the rating on the charger for a reason. You cannot say that their design was flawed or crappy or pathetic if you do not use the device as the manufacturer intended. That they have no control over how you use something after you purchase it is not their fault. It is the consumers responsibility to get the proper charger for the device, or do you think everyone should be audited once a week by the technology police to make sure that you have all your devices, software, and files installed in the recommended way? There is also a third way, where you plug in a device and it tells the power supply what it requires from it and the power supply would then respond to the device whether or not it could supply the requested power. If it could then it would start supplying it, if not the device would get nothing. That would raise the cost of the power supply by quite a bit of money and most everyone would be unwilling to pay extra for the convenience of it. (They have been working on this system of smart power for your home for some time now)

all chargers (but blackberry and iPhones) use micro USB, they should all be the same now. In any case a well designed phone should have input protection to prevent such a thing from happening.