I have TST internal sensors on my trailer tires, I have had them for 4 yrs now. Battery life was supposed to be around 7 yrs, but I've had several of them fail early. First was replaced under warranty, second one cost me $25. Discount Tire did the initial install when I purchased new tires and so far they have not charged me when the sensors stopped working. Just take the trailer in, they dismount the tire, remove the bad sensor and reverse the process. I did not purchase the tpms system thru Discount Tire, purchased direct from TST.
I still run external sensors on the truck rear tires so I can compare the differences. First, the temperature readings are much more accurate with internal sensors. The external sensors are much more affected by sun and wind. Since the internal sensors are more accurate, besides revealing tire temp. they are more likely to detect overheating caused by dry bearings or dragging brake shoes. Anyway, I think they are worth the extra effort.
Larry Day, Texas Baptist Men volunteer
'13 Silverado LT 3500HD D/A CCSB 2wd, custom RKI bed
'11 Crossroads Cruiser 32MK loaded