i need to get a spare charger for my mobile phone?

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Phone manufacturers will frighten you into buying their own make and model of charger claiming that using a different charger will damage your device. Nonsense.

All current mobile phones use around the same voltage. The differences in voltages are so insiginificant that they are indiscernible. As long as the charger correctly fits into the port, it will charge the phone.

I have a 3week old Samsung Galaxy S3 LTE 4G and a 1yr old HTC Sensation XL. Right now I'm using the Sensation XL charger to charge the Galaxy because the Sensation's cable is a bit longer than the Galaxy's and serves my purposes neatly. Both the HTC Sensation and the Galaxy S3 use Micro USB chargers and they swap around perfectly to either phone. I haven't had any problems in the 3weeks that I have been using this charger.

However, having said that, it is obviously safer, for warranty purposes, to use a genuine OEM charger. Should something go wrong with your phone while you are charging it with a different charger to that specified by the manufacturer, that will certainly affect your warranty claim.

So buy your charger with that in mind.

Good luck.
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I find that eBay and Amazon are good for things like that.