The quick version
- LiFePO4 gives you roughly double the usable capacity of an equivalent lead-acid battery because you can safely discharge it to 80-100 percent instead of 50 percent.
- Lithium costs 2 to 4 times more upfront but usually wins on cost per cycle within 3 to 5 years of regular use.
- A 100Ah LiFePO4 battery weighs 22-31 lbs versus 60-70 lbs for a comparable AGM, a real difference when you are near GVWR.
- Lead-acid tolerates a wider range of cheap, dumb chargers. Lithium needs charging equipment set up correctly or it will undercharge, trip its BMS, or age early.
- Standard LiFePO4 will not charge below freezing without a self-heating model or a battery kept in a warm compartment.
I still remember the first van I wired for a client back in 2019, a Sprinter with two Group 27 AGMs bolted under the passenger seat. We watched the voltage sag to 11.9 after one night of running a Dometic fridge and a laptop charger, and she asked the question everyone eventually asks: why not just go lithium? Six years and probably forty installs later, I can tell you the honest answer is not as simple as the ads make it sound.
Both chemistries do the same basic job, storing DC power for when you are off shore power or off the alternator. But how they store it, how much of that storage you can actually use, and what it costs you over time are genuinely different stories.
Usable Capacity: The Number That Actually Matters
Here is the single biggest misunderstanding I run into. A 100Ah lead-acid battery and a 100Ah LiFePO4 battery are not equivalent in real-world terms, even though the label says the same number.
Lead-acid batteries, including AGM and flooded types, degrade rapidly if you regularly discharge them below 50 percent state of charge. Pull them down further and you are chewing through cycle life fast. Most RV and marine techs, including me, tell people to plan around a 50 percent usable rule for lead-acid.
LiFePO4 batteries can be discharged to 80, sometimes 90 percent of rated capacity without meaningful damage, and the built-in BMS will cut off well before anything dangerous happens. That means a 100Ah lithium battery gives you roughly 80-90Ah of real, usable power compared to about 50Ah from a 100Ah lead-acid battery.
Tip: When sizing a lithium bank to replace lead-acid, do not just match amp-hour ratings. A 200Ah lead-acid bank replaced with 100Ah of LiFePO4 will often give you similar or better usable power, at a fraction of the weight.
Weight: Where Lithium Quietly Wins Every Time
A Group 27 AGM battery weighs around 60-75 lbs. A 100Ah LiFePO4 battery from a brand like Battle Born, Li Time, or Ampere Time typically weighs 22-31 lbs. For a two-battery bank, that is a 70-90 lb difference, which matters a lot if you are already fighting GVWR on a Sprinter or Transit build.
I worked on a truck camper once where the owner had stacked four Group 31 AGMs to get the runtime he wanted. He was 400 lbs over his rear axle rating. Swapping to two 100Ah lithium batteries in parallel got him under weight with more usable power than he started with.
Cycle Life and Real Cost Per Year
This is where lithium starts to look less expensive the longer you own it, even though the sticker price is rough to swallow.
| Factor | Lead Acid (AGM) | LiFePO4 |
|---|---|---|
| Typical cycle life (to 80% capacity) | 300-500 cycles | 3000-6000 cycles |
| Usable depth of discharge | 50% | 80-100% |
| 100Ah price (approx, 2026) | $180-280 | $700-950 |
| Weight (100Ah class) | 60-75 lbs | 22-31 lbs |
| Charge time (0-100%) | 8-12+ hours | 2-4 hours |
| Cold weather charging | Works, slower | Blocked below 32F without heating |
Run the math on a typical full-time RVer cycling their battery bank 200-250 times a year. An AGM bank at 400 cycles lasts less than two years before capacity noticeably drops. A LiFePO4 bank at 3500 cycles can run 14+ years in theory, though most owners see real-world lifespans of 8-12 years due to heat, partial cycling habits, and eventual BMS or connector wear.
Divide sticker price by realistic years of service and lithium usually wins by year three to five, sooner if you are cycling hard through boondocking or off-grid living.
Charging Behavior: The Part Nobody Warns You About
A mistake I see constantly: people buy lithium batteries expecting a drop-in swap, then wonder why their old WFCO or Progressive Dynamics converter never fully charges the bank. Lead-acid chargers use a charge profile with a long absorption stage and a float voltage around 13.2-13.6V, tuned to slowly saturate a flooded or AGM battery without boiling the electrolyte.
LiFePO4 wants a different curve entirely: a bulk charge up to roughly 14.2-14.6V, a short or nonexistent absorption stage, and ideally no float charging at all once it hits full. Leave a lead-acid-profile charger hooked to lithium long term and you will either undercharge the bank (never quite reaching 100 percent) or, in rare cases with sustained high float voltage, stress the cells.
Warning: Not all lead-acid chargers are dangerous to lithium, but plenty simply will not charge it correctly. Confirm your converter, charger, or DC-DC unit has a lithium or LiFePO4 profile before wiring it to a new bank. Victron, Renogy, and Progressive Dynamics all sell models with a dedicated lithium setting.
Cold Weather: Lead Acid’s One Real Advantage
This is the honest asterisk on lithium. Standard LiFePO4 cells should not be charged below 32F (0C). The internal BMS on a quality battery, like those from Battle Born or Renogy, will automatically block charging current in freezing temps to prevent lithium plating on the anode, which is a real degradation mechanism, not just marketing caution.
Lead-acid batteries charge more slowly in the cold but do not have this hard cutoff. If you winter camp regularly without insulated battery compartments, you either need a self-heating LiFePO4 model, a battery box you can insulate and warm, or you accept that charging pauses until temperatures recover.
Safety: Contrary to What People Assume
People sometimes worry lithium is the riskier chemistry because they are thinking of laptop or e-bike fires, which typically involve lithium-ion cobalt chemistries. LiFePO4 (lithium iron phosphate) has a much more thermally stable crystal structure and does not tend toward thermal runaway the way other lithium chemistries do.
Flooded lead-acid batteries, meanwhile, off-gas hydrogen during charging and need real ventilation to avoid an explosion risk in an enclosed space. AGM is sealed and safer in that regard, but still needs proper fusing and a case that will not crack under vibration.
Either chemistry is safe when installed to a real standard. Follow ABYC guidelines for fusing, cable sizing, and ventilation regardless of which battery you choose.
So Which One Should You Actually Buy?
If you are weekend camping a few times a year, running minimal loads, and money is tight, a quality AGM bank is not a bad choice. It is forgiving, cheap to replace, and works with charging gear you probably already own.
If you are living in the rig, boondocking regularly, running an inverter for real appliances, or you are simply tired of babysitting a lead-acid bank’s depth of discharge, lithium pays for itself faster than most people expect. Want the fundamentals first? Start with what a LiFePO4 battery actually is, then work through how it stacks up specifically against AGM if that is your current setup.
Before you buy, it is worth running real numbers on what a lithium bank actually costs for your amp-hour needs, and being honest with yourself about whether the upgrade is worth it for how you actually use your rig. There is no universally correct answer here, only the one that fits your camping style, your budget, and how much weight your rig can spare.
