Lithium iron phosphate (LiFePO4) batteries let you use most of their rated capacity, weigh far less, and last for thousands of cycles, but cost more upfront and cannot be charged below freezing unless they have built-in heating. AGM batteries cost less and tolerate cold, but most makers recommend using only about half their capacity, they are heavy, and they wear out sooner. For regular off-grid use, lithium usually costs less over its life.
The house battery runs your lights, fans, water pump and fridge when you are off the grid. Chemistry changes how much of it you can use.
Side by side
| LiFePO4 lithium | AGM | |
|---|---|---|
| Usable capacity | Most of rated capacity | About half, per most makers |
| Weight | Much lighter | Heavy |
| Cycle life | Thousands of cycles | Hundreds of cycles |
| Cold charging | Not below freezing unless heated | Tolerates cold |
| Upfront cost | Higher | Lower |
| Voltage under load | Stays flat | Sags as it drains |
What 100 Ah really means
A 100 Ah lithium battery delivers close to 100 Ah to your loads. A 100 Ah AGM battery should usually be kept above about half charge, giving roughly 50 Ah of everyday use.
Charging
Lithium charges faster and needs the right profile. Check your converter, solar controller and alternator setup, and use a DC-DC charger from the tow vehicle or van alternator where recommended.
Related: RV solar sizing and 30 amp vs 50 amp.
Common questions
Can I drop lithium batteries into my RV?
Often, but check your converter, solar controller and alternator charging. Many need a lithium charging profile or a DC-DC charger.
Can lithium RV batteries be charged in the cold?
LiFePO4 cells should not be charged below freezing. Many batteries include low-temperature cutoffs or heaters; check the spec sheet.
How many amp-hours do I need?
Add up the daily watt-hours of everything you run, divide by 12 for a 12 V system, and add a margin for cloudy days.