When I purchased my 2007 Hummer H3, I noticed that I have a Group 65 battery in it. I researched and found that the Hummer calls for a Group 86. My question is, will it make that much of a difference if I don't change it? And, if I don't, how will it affect the vehicle. Thanks in advance.

 

65 is physically larger and may have more cranking amps.
As long as the battery is secure in the box I see no issues.

 

The metal pan under the plastic battery enclosure is big enough to hold a larger unit.

Upgrading to a larger battery is no big deal.

 

x2, the heat from the engine will overheat the battery, if left unprotected. 65 is 3" longer, oem box won't work.

 

Thank you, all.

 

Welcome bro. Not to worry about expansion....

The stock set up is all eye candy.

 

Research: "heat deterioration"
Many batteries mounted under the hood will have a heat barrier to protect the battery from excessive heat. Make sure that barrier is still in place.