Car battery emissions aren't on the EPA radar yet. I'm not making the case for combustion as better, just saying that auto companies have come a long way since the advancement of the ECU(the engine management system that is now possible and realistic on a mass-market scale thanks to better computing technology to both manage and optimize vehicles). So either way, you're footprint should be a big improvement with a new vehicle, opposed to what you own now. Heck, the last 5 years have been excellent IMO as far as optimizations. Better than the 5 years prior. Coil on plug improvements, drive by wire improvements, recapturing of platinum from various components into a good(and improving) market based system of recycling the materials back into parts. These are improvements on weaknesses the auto-industry had a decade ago, that we are reaping the benefits of today.
Also the sheer fact that the after-market for retromodding is maturing after many years of it being a niche market that was considered a negative by purists and collectors. So the other alternative could also be to improve your miles on that Monte Carlo with something new, if you are truly attached to the car. Something that wasn't anywhere as easy to do in a consumer market full of snake oil in the past(tornado intake BS, magnets on fuel lines, crappy airfilters that claimed to boost power and fuel economy, but only allowed more particles into the engine, BS oil claims, etc). IDK what year and engine your Mote Carlo is, but if you're crazy and love that car to death(like some people and their cars) it's another upgrade to ponder over. Although I would think moving to a decent econobox of your liking would still be hard to beat, since you wont need to put the labor in and you can save on insurance too.
