Originally Posted by
the evil twin
IMHO, given the latest tech and trying to be brief...
You now only need a 2nd 'cranker' spec battery (capable of high current draw) if you want to use it in parallel for winching.
You also only need that for prolonged/regular winching otherwise a good cranker and decent Alt will usually suffice.
For 'emergency' jumps I carry a Lithium Power Pack as they hold charge for yoinks and will happily start my 6.5 Chev, walk up start for 3rd party IE no jumper leads and also run a lappy or whatever for quite a few hours.
The above means you can use a lower max current spec battery for vehicle aux or camper/van house applications and they are usually up to 20% cheaper.
Cheapest solution is AGM and fine if weight, space, voltage sag and cycles aren't an issue.
Best solution ATM is Lithium (by a mile 'cept for initial cost) especially for voltage sensitive stuff and you will get equivalent use out of a battery approx 40% smaller so when comparing price a 60AH is approx equal to a 100 AH AGM.
It/they will also last much longer but a lot of us may not see that advantage in reccy use but it means the bottom line over extended time is the Liths are now almost equiv to AGM in price.
If you get one that has the 'onboard BMS' most refer too then any charge source is equally good for either tech.
Charge sources (when not using as a 2nd cranker/wincher)... IMHO again...
Aux in vehicle... Battery Isolator only
Aux in vehicle and solar panels... Battery Isolator and dinky little quality Solar Controller or genuine full MPPT if you really want
Aux in trailer/van... combo DC/DC MPPT multiple input Controller