The lithium batteries are more efficient at high discharge rates, so for equal "starting power" (generally depicted as PbEq or lead-acid equivalent amp-hours) the lithium is smaller, with less reserve capacity.
That "Pb-Eq" marketing term can be extremely misleading, and more than one builder/pilot has been surprised to find out that their new light-but-expensive "equivalent" LiFePO4 battery will power their avionics/EFI for a lot shorter time after a power failure than their old lead acid battery did.
More from a post by RV7Charlie here:
Any experience with Lithiumax start batteries?
Folks need to look at the discharge charts. They also need to consider the impact of a BMS failure/cutoff when thinking through alternator failure scenarios. There are times when flying that we just might not care about preserving battery life and instead want the battery to provide electrons down to 8 volts, and will be happy to buy a new one upon getting down safely.