Is it bad to Charge my Ipod with a non-apple charger?

At first I didn't use any other charger except my apple usb connected to the computer…

but now i started using a non-apple nikon charger that says 'Input: 100-240W"

I started noticing my battery died quite quickly… I'm a bit confused

anyone mind explaining how much Watts has the USB-Computer Apple cable?
Am i overcharging it with the wall nikon charger?

Its bad because the charger is giving way too much energy to the Ipod when charging. When you do this the battery life dies faster. You should use the regular Ipod charger. Hope I helped.