Modern electronics use Lithium-ion batteries. Li-ion batteries are only good for so long, and can only be charged so many times. Over time they simply lose the ability to hold any charge.
Find someone with the same device as yourself and try their battery in your phone, and your battery in theirs. If your phone turns on, but theirs doesn't - you know it's the battery.
If your phone does not turn on, but there's does (with your battery inserted in their device), it indicates an issue with your phones hardware. Most often this can be caused by dropping the device, and having an internal connection come loose.
Also, while your battery is in their phone and vice versa, plug both phones in and see if they both charge. If your phone (with your friends battery in it) powers on, but will not charge, this again indicates an issue with the hardware of your phone - specifically a broken charging port.
One last thing you could do, is to get a multimeter and check the voltages of your charger, phone and battery terminals.
Facebook
Twitter