Arduino micro- USB port to charge a 9V battery

was wondering if it was possible or if anyone has been able to charge an external power source as in a rechargable 9V battery via the micro usb port. and have the circuit running from the external power source when not connected with the usb? :slight_smile:

Describe what you want to achieve. Which Arduino do you have in mind? The Leonardo and the Due have micro USB ports but both lack the circuitry to charge a battery. The Seeeduino Stalker (Seeeduino Stalker | Seeed Studio Wiki) has battery charging on board but for a standard lithium battery (3V7) and not a 9V type.

the arduino micro. it has a micro usb port im going to run my circuit with a 9V battery but thought it could be pretty cool if i could use the USB port to recharge the battery cant really use an arduino thats any bigger as my project is rather small...

Don't try to load alkaline batteries, they are not built for re-charging and may explode.

The Micro doesn't have a battery charger on board so you need additional circuitry to charge. I would recommend something like this: Lipo Rider Pro | Seeed Studio Wiki. Of course this does not use a 9V battery but LiPo batteries are lighter and deliver much more energy than a 9V block battery. BTW: you loose a lot of energy if you provide 9V to the Micro over the Vin pin. About half of the energy in the battery is wasted for heating the board by the linear voltage regulator.