I think they used to make a gadget that plugs into a cigarette lighter to keep memory alive during a battery swap but with some of today's cars shutting off the lighter socket for some reason it may not work without some work.
I use one of these. Just a raw, 4S LiFeP04 chemistry RC hobby battery to jump start V-8's with no issues at all. The extra Volt makes a huge difference in actual starter motor speed. No circuitry, no caps, nothing but the raw battery.
The thing about LPF, is that there is practically no self discharge so you can leave them topped up without damaging the cells. No so true for lithium Ion or Polymer. Number of charge cycles is at least twice, up to 4 times as many before capacity loss.
A few years ago, I tried some microstart brand units. After a year, they swelled so I opened them up. They would add the cells In-Series AND in-Parallel and give a completely false battery capacity figure.