I've run it on the magellan cradle with no batteries and had the same problem. Only thing I haven't tried is screwing the power chord into it and running it on the ram cradle. If it's vibrating the batteries that bad though, it's going to really cut into the life of the thing. The batteries don't actually come "loose" or anything, but may be vibrating against the contacts so as to be on/off/on/off, etc... What speeds have you run it at and for how long? My first meridean I ran on the magellan cradle and it worked at first but the speed at which it would work kept coming down and down until I could hardly use it while riding. That unit was still fine otherwise and didn't necessarilly need replaced, I just chose to give it to someone. So now I'm on number 2... same problem. I guess I'll live with it in the map pocket and be happy I've found something that works at all.