can i use 4 rechargeable aa batteries for a usb charger?

I found a lot of portable usb charger Instructables using a 9v and a 5v regulator and one that used 2 aa with a 5v boost converter. if I'm using it to charge a device that uses a 3.7v li-ion, then wouldn't any voltage above that work, so as long as it's not high enough to damage whatever it's charging? so would putting 4 aa (4.8v) with just a capacitor and diode work as a safe portable usb charger? or does it need to be exactly 5v?

110100101108 years ago
4 rechargeables without diode are ok to charge usb. check with volt meter that the voltage really is not above 5.25 V (the max allowed for usb devices) a diode takes away 0.7 V. another diode inside the device takes away 0.7 V more. 3.7 V li-ion cant be charged with 3.4 V
Andrew_486 years ago
i have make a similar charger were i use 4aa rechargable batterys ,a diode ,and a 100mF 25v capasitor and belive me it works very well for a portable charger and becose batterys are 2000mha i am able to charge up to 3 devices and yea it doesn't need to be exactly 5 volt .

if you want i will post some photos and also a diagram if you want to make it :):)
Thermiter7 years ago
Definitely DON'T do that!  Nearly all USB devices use 3.7v Li-ion batteries (iPhones, iPods, cell phones), but they have internal charging circuitry because of the unique charging demands of lithium batteries.  If you feed that circuitry less than 4.75v, it will not function properly and may break.  You MUST supply a regulated 5 volts to any USB device or it will not work.