We do suggest investing in an external battery charger as IJOY does not recommend charging external batteries with the mod through the USB Port. External chargers have a much more reliable chip when compared to box mods. Box mods with USB internal chargers are fragile and can get damaged with day-to-day usage while your external charger is safely stowed at home. The internal charger has a much higher chance of going faulty with regular usage when compared to a standalone external charger. Also, unlike box mods, your batteries will not be enclosed during charging. External chargers are designed to dissipate heat and are crucial to keeping your batteries cool and safe. Some external chargers will also monitor the temperature of your batteries and will cut-off if they become too hot. You want your batteries to reach a maximum 4.2 volts capacity or slightly below, but the key here is accuracy and consistency. Overcharging is potentially dangerous and bad for the long-term life of your batteries as well as can cause damage to the charging components on the box mod.
Cell phone chargers or car USB chargers often provide more power than needed which can cause overheating and damage to the USB port. Computer USB ports can vary in how much charge they deliver please make sure you use a port that supplies a safe amount of power for recharging vaping devices. Do not use USB3.0 or 3.1 for charging as these ports can provide more than 1 amp of current.