Usually it's not a problem, but I have encountered two power tools that gave me issues draining the batteries. One was not a Festool (can't remember which brand or which tool) and it definately drained the battery over 6-12 months. The danger is once the battery gets too depleted, it won't charge without resorting to Frankenstein tactics. The other was a TSC55, which had not been used for 8 months. I know the batteries had a charge when it was put away. One battery was low, one was depleted and gave me errors when I tried to charge it. I don't know if it was just a flaky battery, but I just take the batteries out when I put it in the systainer.
Mostly I remove the batteries from any kind of saw so they don't accidentally turn on if I'm moving them or bump a switch. They all are stored with a blade. Drills I don't worry about because I don't leave them with bits in them. But I haven't seen any other power tools deplete batteries on me.
I have seen some of the other shop tools deplete the little coin batteries in them. I have a lot of stuff that gets used once in a blue moon, so I have to pull the batteries from them (depletion or leaks). The last victim to a leaky battery was a fluke non-contact voltage detector. That mistake cost me $20. Oh, and I throw out the cheap chinese batteries that come with tools and install a name brand battery (just in case I should forget to remove it). 90% of the time, the leaky batteries have been the freebies included with the tool. Of course, 90% of the time I used the cheap chinese battery supplied, so maybe that means nothing?
