Macka, I'm happy with my Doran TPMS. The sensors (which I've got mounted on the stems, but there's an internal system which may or may not use different sensor) have a non-replaceable battery, but are supposed to last a couple years or more. The one I bought had been owned by someone else on the Forum for a couple of years, but he had never mounted it. I had it for several months before I got around to mounting it and then a few months later the battery on one of the sensors failed while I was riding to Alamo, NV, for my Bun Burner Gold attempt.
I ended up disconnecting the monitor from the Fuseblock so I wouldn't have to watch the alert light blink red. I think I paid about $40-50 for another set of sensors and it's worked fine since then. You can leave the monitor hooked to a powered circuit and it will show pressure even before you start the bike. But the monitor dragged my battery down after 5-6 days, so I've got it wired to a switched circuit now. The sensors send a signal every six minutes, so they
may start showing results almost instantly. I don't sit around waiting for them to show up, but when they connect, I check pressure.
The Doran system isn't temperature compensated, but I know what to look for after the tires have warmed up. I'm happy with it.
Link to manual covering installation and use:
http://www.doranmfg.com/sites/default/files/360M manual (v2.1)--.pdf