Motorola RAZR V3

Does anybody know how much extra batter power is used if the bluetooth is left on? I'd prefer leaving it on all the time rather than having to manually turn it on each time I get in the car (to connect to car's integrated handsfree), but I'm wondering if that takes a significant amount of battery life away. The manual says that leaving bluetooth on decreases batter life, but it doesn't say to what extent. Any ideas?

Thx,
Tom.