Micro USB Charge: BESTON 9-Volt batteries can be charged by any USB 5V output like wall chargers, power banks, it does not need an extra charger Stable Voltage Platform: Unlike alkaline 9V battery's 9.6V to 5.4V output voltage, lithium ion 9V rechargeable battery has stable 8.4V to 6V discharge voltage platform High Capacity: Our 650mAh 9Volt rechargeable battery has more power capacity than alkaline 9V battery (about 500mAh) Long Life: They can be recharged more than 500 times, make them a economical replcement for primary 9V batteries This battery can only recharge to 8.4V. If your devices like smoke alarm require standard 9V or higher voltage battery, please buy standard Alkaline 9V Battery