I've seen a lot of topics on the forum regarding Optima batteries. Most indicate that to install an Optima, you have to cut the battery tray and also the bracket holding the ECM. The reason for cutting the tray is that the C4's use a group size 75 battery that is about 1.5" smaller than the Optima group size 78 that was the closest available. Optima just recently began production of group size 75. If you're in the market for an Optima, make sure you get the right size.

The reason for cutting the bracket is that the Optima is a dual terminal (both top and side posts) battery and the top posts get in the way. This might still be a problem because the new size 75 is still dual terminal. I did hear that they were going to produce a side terminal only size 75 in the next 6 mos, not sure if this is reliable though because all their other batteries are dual post.

The Optimas are constructed much differently than conventional batteries and have cycle characteristics that are very well suited to cars that are driven on a limited basis and stored for extended periods. :flag

 

I have an optima in my 89 I know the 90 and up have the cpu on top of it but I didnt do any cutting just poped it in there, It was also the only battery with side post I could buy here in japan on short notice I also bought it on base...
oh well no biggie I like it no problems at all.. :cheers:

 

I just installed an Optima, the 75 series. Other than snipping two small plastic pieces in the tray, the fit was good. The top posts were more of a concern, the positive one was too close to the ecm/cruise bracket you refer to, it would've worn through the plastic terminal cap and shorted out so I bent the bracket just enough to have adequate clearance. Optima should've come out with a side post only battery long ago, there are many other cars that have the clearance issues like this.