Just a quick update to this thread. After several months of driving around with this larger Group 34R battery I can report having ZERO issues or problems with it. The battery has not moved at all, it fits perfectly and having all that extra storage capacity and cold cranking amps during the winter is a definite and very tangible bonus. I encourage any HHR owner who could benefit from having additional battery capacity to make this upgrade.

And just out of interest, how many others have done this upgrade?

 

I should also mention that the battery I went to was an AGM. AGM batteries don't offgas like old-school flooded lead-acid batteries (see https://www.cdnrg.com/blog/flooded-v...agm-batteries/) so you don't have to worry about not being able to use the OEM vent tube with it if that's a concern for you. Honestly, this is such a great and easy upgrade. I will never consider putting anything but a Group 34R AGM battery in my HHR again.

 

ok thanks DangerBoy, good info

 

The 650 cca & 710ca I installed in mine is same size battery (I'm told) that is in the ZO6 Corvette.

 

Attempted summary of above, plus current Googling, Menard's pricing shown below:
OEM battery is ACDelco "Advantage:, 36 mo warranty, Group 90 (T5), 710CCA: $140 from Menards, before tax, rebates, core refund.
Ditto of above Group 47, 785CCA: $135
Ditto of above Group 24R, 720CCA: $128