A couple of points on batteries:
"Traditional" batteries are lead acid (also referred to as Pb - element sign for lead). They come in several flavors, flooded, sealed, AGM (Absorbed Glass Mat). Those intended for starting engines are designed with thin lead plates so they can put out lots of current for a short time (referred to as Cold Cranking Amps). Then there's deep cycle batteries that are made with thicker plates to deliver a lesser amount of current (than cranking) for a longer period. So you can probably tell that the ideal starting battery won't be the same as the ideal long term (e.g. trolling motor) type.
That said, in the case of sxs, we'll have a starting battery and the aux will be a compromise if we are going to run a winch from it, as the winch will draw upwards of 100 to pushing 200 (depending on size and load). Besides, I'm not sure you can even find a deep cycle marine battery in a size that will fit in most sxs!
Pb batteries provide longest service when they are not discharged below 80%. 50% is the recommended low limit. Lithium batteries, and the more "fire safe" lithium ferrous phosphate (LiFePO4) types, can be regularly discharged down to 20% and lower, so their real capacity far exceeds Pb. "True" battery isolator/chargers, that many here use for connecting the two batteries, makes a version specifically for using a Pb main and LiFePO4 aux battery (I have no experience with them, just with their Pb to Pb "standard" version which works well).
There's much more, but I'm running out of steam.
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And there's lot's more info to be had by searching this forum.
best,
bumper
