NEVER BUY BATTERIES AGAIN, use this commercially produced 40” USB power cord to run the fan from a rechargeable power bank, power box, USB battery adapter, etc.. Nothing on the market with the correct plug on the I made them by retrofitting the plug end to perfectly fit the jack on the heater. USB conversion mods on the internet require you to open up the back of the unit and splice into the heaters wiring.......mine is simply PLUG’N PLAY, remove the batteries and plug it in! Fan still performs excellent on 5v instead of 6v.......$22 mailed to your door!