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When you say Lithium, you perhaps should qualify it as multiple types of Lithium batteries exist and they behave differently.
It might be a battery people often use to power a mobile etc. They usually use the same technology as lithium batteries in cameras, mobiles etc which is Lithium Cobalt. (and can also explode etc as a mobile battery can do)
Lithium batteries used in the RV/Camping industry are usually Lithium Iron Phosphate (or LiFePO4) - BTW - Which don't explode
Don't use a Lead Acid battery charger on LiFePO4. It just will not fully charge no matter what the advertisement may claim. It will also not charge as fast as a charger with a Lithium charging profile (because lead-acid chargers have an anti sulphation phase). Depending on the battery specifications, unlike lead-acid batteries, the charge voltage will need to be around the 14.5v. A charged battery will be around 13.8v (ie. 12v is a nominal voltage).
Understand your load - i.e. Know what the max current draw from the battery. Multiply the load by the time to get a rough capacity requirement.
Target a 50% depth of discharge as you will get a lot more discharge cycles from the battery at this rate and it will give you some wriggle room if say your dew heaters use more that night or you want to spend a bit more time in the field or that new camera uses more power to heat to your new lower temperature you decided to run at that night.
LiFePO4 have a reasonably flat discharge curve so measuring the voltage to get an idea of it's charge state is a bit useless. Either get a battery with built-in capacity level monitor (such as Enerdrive or Invictor with associated mobile app via Bluetooth) or use a lithium compatible battery monitor (with appropriate current shunt) from Enerdrive or Victron (and not a cheap junk monitor built for lead-acid batteries)
So LiFePO4 with a proper lithium charger (such as a Victron charger) charging close too but under the max charge rate specified by the manufacturer is the best. Fully charge at the beginning of each session is the best at keeping the DOD small.
Having a built-in capacity monitor is the easiest way to go
Understand your load. It's no good buying a battery based on the physical size and expecting it to carry your load.
Don't forget to fuse the positive as close to the positive terminal as possible with an appropriate fuse to protect the wiring (from shorts etc)
Keep the battery as close to your gear as possible and use the thickest wire possible to reduce voltage drop.
Think about using anderson powerpole connectors (Rigrunner is a good example of a fused solution) in place of the cigarette style connectors.
I hope this helps with the lithium battery discussion
cheers
Greg
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