yeah, it could be the motors. Did you by chance break them in? That could help, also if you have run several packs through them a day, that could be wearing on it as well
About the batteries, do you have a volt meter? If so charge the packs and get a voltage reading off of them. If it's 8.4 you're golden, if it's below 8.3, then your charger or battery has a problem.
also look at this page under the cx2 section
http://www.heli-max.net/mediawiki/index.php/Index:HOWTO