Many laptops had both a lithium ion battery and a watch battery used to keep the bios and an internal clock running after the battery died. https://www.makeuseof.com/tag/why-does-my-motherboard-have-a...
Both lead acid and supercaps are not even remotely comparable to the main liion battery, they're suppliments, and not interesting ones
As for 12V, all one needs is a regulator. Unless you have a long-term supply contract (that, I bet, won't be renewed for too long), a lead-acid battery is just dead weight.
https://insideevs.com/news/546087/tesla-liion-12v-auxiliary-...
When Sandy Munro interviewed Elon Musk a couple of years ago he said "Why are you still using 12v stuff in the cabin?"
Musk's answer was that the automotive supply chain was entirely geared around 12v equipment and they had to take advantage of that to get to market quickly.
I'm glad those days are almost over.
This seems like an odd choice - unless you already bought a supply of lead-acid batteries for the next 50 years or so.
I've read about a car using supercapacitors in the regenerative brakes to capture energy at high current and, then let it trickle back into the main batteries (or drivetrain) at levels that won't damage it.