iPhone 3g & Griffin iTrip - works but iTrip looses power after approx 1hour

I went into Halfords over the weekend as I had a 3 hour drive to London and wanted to listen to my music.

In store I tried a Griffin iTrip with my iPhone and the stores numerous headsets and it worked (got the standard "not compatible" message when connecting it but just ignored this).

Anyhow, approx an hour or so into my journey the iTrip which is powered by the iPod/iPhone looses power. I pause the music and press play again and the power comes back only to drop out again approx 1 min later.

This continues to happen to the point where I can't keep doing it while driving cause it would be dangerous.

On my journey back, the same thing...approx an hour into the journey the iTrip looses it's power and i'm back to square one.

Anyone experienced this? I know they're technically not compatible and so I'm thinking I'll take it back but I just wondered if it was a faulty iTrip or if there is something going on behind the scenes of the iPhone that is cutting the power off after a set amount of time?

I've also had the iPhone plugged into a 3rd-party set of speakers at home and I get the same message about compatibility but this continues to work past an hour (although the speakers have their own power supply).

Cheers


Wayne