I have been having problems with my power connection. HP had my computer from 8/2-8/12 and 8/16-8/24. On the second repair they swapped out my motherboard. When they did they gave me a 120 Watt powercord instead of the 90 Watt one. I assume that means the new motherboard uses more power. It seems to be the case since they say they did not swap my battery and my batterylife has fallen from 3.5 to 2.5 hours although my full system backup time has fallen to 4:10 from nearly 5 hours.
It might draw more power, but I kind of doubt it... I think they'd be much more likely to install a motherboard identical to the original one, particularly on a laptop where not many different types would fit properly.
It's possible they just sent a 120w power supply because they ran out of 90w ones, and the power supply needed to be replaced.
As for loss of battery life... It could be increased power draw, but gradually decreasing battery life is typical for aging laptops.
Agreed it would be strange for them to swap with a higher power hungry motherboard (if that even exists). My only thought is that maybe they upgraded your processor as a thank you or something. That would cause your symptoms. Just check your processor see how fast it's running and whether or not it's different than before (of course that means you need to know what it was before).