Good idea in theory, but in reality it is hard to read because of angle of windscreen. Also, the sucker tab will not keep it in place - falls off window and dashboard - sucker needs to be made of real natural rubber (not plastic). I managed to get it to stay in place by using "blue tac". Would not buy again - not practical.
Clock arrived in 3 weeks, all works, No info about suitable battery (LR1130 can be used)