CharlyE500

Hi guys,
Need some advise. I am thinking to change my battery since bought the car last March and not driving much. (total about 1K miles)
Last time drove was 2 weeks ago and this morning I felt harder to start.
So I went to Costco and check their battery department book shows 2007-2012 Starter battery is H6(48) AGM Interstate and Trunk battery H8(49) AGM.
I like to make sure they both OK with my car. I read some thread says the Starter use V4 size....
Any feed back will be great. I know need to unplug the trunk battery before the starter battery, once change starter i can plug the rear back on.

Thanks