As another data point, I currently have an Odyssey PC680 in the baggage area of my RV-3. Since purchasing the plane a little over 5 years ago, I’ve swapped out to a much lighter constant speed prop. My CG is a little more aft than I’d like with the prop change and a little baggage, so my plan is an EarthX vented battery mounted on the cool side of the firewall on top of the tunnel between the rudder pedals. I’ll fabricate an airtight box with venting to the underside of the plane in case of battery malfunction. In my mind, this will remove the weight of the PC680 and about 4 feet of heavy wire and will add just a few pounds forward of the CG. I’m estimating it should save about 15 pounds in total weight.
For what it’s worth, I’m also installing an EarthX battery in my Glasair 1RG as part of a big avionics upgrade. It’ll go on the hot side of the firewall and will be contained within the heat shield battery box that EarthX sells. I’m pretty sure the model number on the Glasair battery is 680C. It’s their compact battery.
Both planes have B&C 40 amp alternators and B&C voltage regulators.
Battery choice has almost become the equivalent of the Primer Wars of days past, so I’m actually a little hesitant to post!