One of the many issues when using drop in lithium batteries and relying on the built in BMS inside the battery to do all the protection. A very expensive lesson if/when it all goes pearshaped because the internal BMS wasn't really up to the job.
around would be to use the power supply mode on the charger (if it has one) because that will not try to use clever programming that is suited to lead acid batteries but not lithium batteries. Power supply mode is generally 13.8v and max current
is the capabilities of the charger if below 13.8v and tapered to maintain that voltage. 13.8v = 3.45v per cell in a 4 cells in series 12v LFP lithium battery ... well if they are all perfectly balanced that is, it can also have one cell above the damage danger
zone of 3.6v and the other at what ever combination makes up a total of 13.8v. Far less likely to damage a cell using the lower voltage and allowing the internal balancer to do its thing over how many days it takes to get the cells top end balanced ..... the best of them balance at 0.5 amps, that means it would take 2 hrs to shift 1Ah imbalance between two cells, many are 0.05 amps capacity, so 20 hrs to shift 1Ah. If the cells have been high voltage charged (above the 3.45v average across all cells) then the out of balance in the top balance will be a lot more than 1Ah.
The next issue is what cell voltage the balancers actually start working, some of them don't kick in until the cell reaches 3.85v ..... because they were originally designed for LiPo cells which have a higher nominal voltage and higher fully charged voltage, 3.45v for LFP and 4.2v for LiPo, charge the LFP cells to 4.2v and you will need new cells real quick, holding the cells at 3.85v just means it takes a while longer to need new cells.
As far as using lithium batteries as start batteries, the heat in the engine compartment would be the only problem with proper lithium batteries, if the drop in lithium doesn't have the current
capability to act as a starter battery then the question has to be asked ..... why? A proper 100Ah lithium battery built up from 4 x 100Ah cells in series can deliver over 500 amps and a continuous 300 amps for 20 mins, if it doesn't start after 20 mins of cranking then the battery is the last of your problems :lol: I'll attach a link to the Winston Thundersky 100Ah cell to show you the chart that verifies the 300 amp continuous and still get all 100Ah capacity, multiple the single
cell voltage by 4 to get the terminal voltage for a 12v 4 cells in series battery.