9V Rechargeable 650mAh Li-ion Battery with Micro USB Charging Port - 4 Pack. These have proven to work very well. I have used them in a couple different applications so far, and they have held up well. Charge lasts a good long time, and no issue with the amount of power at all. It is also very easy to charge them with just a typical android charger.... Would recommend them to my friends. #Viralix #Keenstone #Keenstone2018@