Topic: 3DS Charger Question

I heard that the official 3DS charger operates at a DC output 4.6 Volts and 900mA. (Although I'm looking on eBay and the battery's voltage is 3.7? Um what?)

I'm looking into non-standard chargers and reserve battery supplies, and I've found two general purpose reserve batteries: one is a miniature, 2,600mAh capacity battery that charges at 5 Volts, 800mAh, (which is exactly what the iPhone charges at) the other is a whopping 50,000mAh capacity battery that charges at 5 Volts, 1,000 mAh. Would it be unwise to charge a 3DS with these batteries, or is the difference negligible?

If it is not, if I have a third-party charger for the 3DS that converts Power Point to USB, and then use that to charge the reserve battery at 4.6 Volts, 900mAh, (under the second battery's capacity) could I use that undercharged battery to charge my 3DS?

On the same lines, is it perfectly fine to plug a direct USB/3DS charger from your PC tower to your 3DS? Or should I be looking up the Voltage/Amperage of it?

EDIT: I just checked the charger I'm currently using: It puts out 5.2 Volts at 800mAh and I haven't had a problem with it.