I did find an article on a Paramedic site about how even a small LiFePO4 battery in parallel keeps a lead acid battery charged to perfection. Basically it's like having an on board trickle charger. It was recommended for Ambulances in small towns that may not get used daily.
There are a lot of LiFePO4 STARTER batteries appearing - do NOT get these confused with often cheaper deep storage batteries, which DO NOT DUMP DISCHARGE.
I have never (temping fate) had an issue starting in any temps - but mine sleeps indoors.
Bigger starters - NEED more amps. Basic electricity.