I bought the TST system with replaceable batteries and the sensors you can add air thru. I am not happy with the system as I was told by the company (TST) that it can take up to 20 minutes to get a reading and sure enough on one of my sensors it takes forever to get a reading. So much for checking my tire pressures before leaving camp. Also, one of the units falsely indicated a complete loss of air on one trip. Only did it once but I no longer have confidence in the system. Feel like I wasted my money.
