just had a chance to get it working. I pulled out a 30 foot Jayco trailer and ran it on my house battery connected to shore power. The pressure in my trailer tires gradually dropped, dropping to 70psi. I first tried stretching the device onto the back of my trailer to fill the spare but that didn't work. I have to pull out the spare tire to reach it. Not that it's terribly uncomfortable, but something. It reaches the tires of my four axle trailer when connected to the trailer battery. Operation is simple: connect to the battery. Screw the air hose to the pump cable. Screw the end of the air hose onto the tire nipple - the pressure gauge shows the pressure in the tires. Turn on the pump. When the tire has reached the desired pressure, turn off the pump. Disconnect the air hose from the tire and repeat the process if necessary. This device inflated all five tires to 80psi according to the pressure gauge on the device. I switched the device on and off separately for each tire only to fill it with air. The device did not overheat and appeared to function normally. All products fit back into the supplied case, which I always carry in my truck. I'm pretty confident that this product will work in a traffic situation if needed. Something I hope not to experience by buying a tire pressure monitor. Product improvements I would like: Longer battery cable. Air on/off switch on meter.