Playing PS2 games drains the Sixaxis battery faster?

I'm really happy that I can play PS2 games on my PS Tripple, granted, I live in Sweden the machine only uses the software emulation used in the PAL units. Still, it's always nice to see those favorites from the past blown up to HD resolution.

Anyway, is it just my imagination or does playing games using backwards compatibility drain the battery of the Sixaxis/DS3 faster? For example, while going through another replay of Resident Evil 4 the PS3 tells me the battery level is low, showing the charge bar totally empty. Exiting out to the XMB shows the same bar with one line left. Getting the same information while playing a proper PS3 game and then exiting to the XMB the battery charge level is correctly shown empty indeed.

This is stuff you noticed when summertime hits and you have too much time on your hands, and too few new games to get your claws on. This calls for a thorough investigation.