We just today received this message from our campus email administrator with regards to IBM Lotus Notes Traveler, which is the Exchange/ActiveSync interface for communicating with our campus IBM Lotus Domino servers using an iOS device:

A special note about the new Reminders feature in Apple iOS5 - Some users are noticing a quicker battery drain following the upgrade to iOS5 on their Apple device. Lotus Notes Traveler does not yet support the Reminders feature, so creating a Reminder list will cause constant polling and drain the battery. We suggest this be turned off. To do this, navigate to Settings – Mail, Contacts, Calendars – IBM Lotus Notes Traveler for – Reminders – OFF.

I have not yet upgraded to iOS5, so I can not test my theory, but I wonder if the same problem exists for Google accounts that are being accessed via Exchange/ActiveSync (as opposed to IMAP).
If Reminders is listed in the settings for your Google account, I would try turning it off.
Again, This is just a theory. I have not yet tested it