The DC Electrifier uses up to 5 milliamps electrical current which drains the batteries fairly quickly. In order to not have to change the batteries every week it is best to order this add-on feature which allows you to plug the AC adaptor into the recharge jacks to recharge the batteries in 3.5 hours. There are two jacks. Each one connects to two of the four batteries. So unless you buy another AC adaptor from Mouser Electronics (Mouser #553-WDU15-1000 $11) then the total charge time will be 7 hours. The normal DC Electrifier does not come with the necessary jacks to connect to the batteries. Yes you can buy your own rechargeable batteries and recharger but having to unscrew the box cover and remove the batteries each time is a hassle. The supplied AC adaptor (15v/1A, USA prongs) requires 120v AC, so if your voltage is 240 volts or of a different plug type then you will need an adaptor to make it work.