I use the BP-511 battery and I have acquired a lot of 'em over time (I've had three different camera's: 20D, 40D and now a 5D and they all use the same battery) and also got a bunch of the backcaps. I always use them, but they piss me off; a lot. I'm not consistent enough to always put it on the right way so you can see if the battery is full or empty. Any disadvantages to not using them? Probably not right?