Lithium vs AGM Batteries: Usable Capacity Decides It
A 100Ah LiFePO4 battery gives about 85 usable amp-hours, while a 100Ah AGM gives about 50, so the two are not comparable at their nameplate. Over service life LiFePO4 delivers energy at roughly $0.07 per usable kilowatt-hour against about $0.73 for AGM, a ten to one difference, and AGM only wins for unheated winter storage, very occasional use and the tightest budgets.
Two batteries with the same number on the label do not hold the same amount of usable energy, and that single fact settles most of this comparison. Buy LiFePO4 unless the vehicle sits unheated through a freezing winter with no self-heating pack in the budget, or unless you camp so rarely that no battery will ever reach its cycle life. A 100Ah lithium pack gives you 85 usable amp-hours; a 100Ah AGM gives you 50, and it weighs two and a half times as much to do it.
Depth of discharge is where the argument starts. It is the fraction of a battery you can take out before you are damaging it rather than using it. LiFePO4 is conventionally worked to 85 percent, and cells tolerate that daily for thousands of cycles. Lead acid, including AGM, is worked to 50 percent, and every trip below that costs measurable service life. The manufacturer of an AGM battery will tell you the same thing in the datasheet, in a table of cycles against depth of discharge that falls off a cliff.
What do you actually get from 100 amp-hours of each?
Set the two side by side on every specification that changes a build. The nameplate row is the only one where they match, which is exactly why it is a bad basis for a purchase.
| Specification | 100Ah LiFePO4 | 100Ah AGM | Why it matters in a vehicle |
|---|---|---|---|
| Nameplate capacity | 100Ah | 100Ah | Identical, and this is the number that misleads people |
| Safe depth of discharge | 85% | 50% | Going deeper on AGM costs cycle life immediately |
| Usable amp-hours | 85 | 50 | The only capacity figure worth designing around |
| Usable watt-hours | 1,088 | 600 | 12.8V nominal for LiFePO4, 12.0V for lead |
| Typical weight | 22 to 30 lb | 60 to 70 lb | Roughly 35 to 45 lb of payload per 100Ah recovered |
| Cycle life at rated DoD | 3,000 to 5,000 | 400 to 600 | Six to ten times the service life |
| Charge acceptance | 0.5C to 1.0C | 0.2C to 0.3C | 50 to 100A against 20 to 30A on a 100Ah pack |
| Time to refill from empty | About 2 hours | 5 to 7 hours | The taper above 80 percent is what costs AGM the time |
| Self-discharge per month | 1 to 3% | 3 to 5% | Matters over a winter of storage |
| Charging below freezing | Not without a heater | Yes, at reduced rate | The one place AGM genuinely wins |
| Off-gassing in normal use | None | Minimal, vents under abuse | Both are acceptable in a living space, neither is sealed forever |
| Voltage as a fuel gauge | Useless, 0.6V span | Workable, 0.9V span | Lithium needs a shunt to be legible |
The usable watt-hours row is the one to sit with. LiFePO4 stores at 12.8V nominal and lead acid at 12.0V, so the energy gap is wider than the amp-hour gap: 1,088 watt-hours against 600. To match a single 100Ah lithium pack you need two 100Ah AGM batteries, which is roughly 130 lb of lead, two trays, two sets of cable and a parallel connection that has to be built symmetrically or one battery will do more of the work than the other.
Weight is not an abstraction here. A hundred pounds of payload is a full water tank, a rooftop tent, or two people's gear for a week. Every build eventually meets the number on the door jamb sticker, and battery chemistry is one of the few places where you can buy the weight back without giving anything up. Work the totals in the payload weight calculator before you commit to a lead bank.
What does each chemistry cost per usable amp-hour over its life?
Upfront price is the wrong comparison and it is the one everyone makes. The right comparison is what a battery costs per unit of energy it will deliver before it needs replacing, because that is what you are actually buying. Cycle life figures below are published class-typical values at the rated depth of discharge for each chemistry, and the AGM price is a representative street price for a 100Ah Group 31 rather than a specific listing.
| Battery | Price | Usable Ah | Cost per usable Ah | Rated cycles | Lifetime kWh | Cost per usable kWh |
|---|---|---|---|---|---|---|
| Typical 100Ah AGM | $220 | 50 | $4.40 | 500 | 300 | $0.73 |
| Lithova 100Ah LiFePO4 | $144.39 | 85 | $1.70 | 2,000 | 2,176 | $0.066 |
| Renogy 100Ah self-heating | $299.99 | 85 | $3.53 | 4,000 | 4,352 | $0.069 |
| Litime 100Ah | $365.99 | 85 | $4.31 | 4,000 | 4,352 | $0.084 |
| Renogy 200Ah Pro | $809.99 | 170 | $4.76 | 5,000 | 10,880 | $0.074 |
| Litime 320Ah Mini | $763.59 | 272 | $2.81 | 4,000 | 13,928 | $0.055 |
Two things jump out. First, lithium is competitive on day one and not merely over a lifetime. A Lithova 12V 100Ah LiFePO4 Battery (Group 24, 100A BMS) delivers usable capacity at $1.70 per amp-hour against $4.40 for a typical AGM, so even before a single cycle has been run the cheap lithium pack is the better value on the metric that matters. The premium packs land near AGM on that same column, which is fair, and then win overwhelmingly on the next one.
Second, the lifetime column is not close. AGM delivers energy at roughly seventy-three cents per usable kilowatt-hour, and LiFePO4 delivers it at five to eight cents. That is a factor of ten, and it comes from two multipliers stacking: lithium uses 85 percent of itself rather than 50 percent, and it does so six to ten times as many times. A Litime 320Ah Mini at $763.59 is the cheapest energy in this table by a clear margin, and it also removes the parallel-wiring problem entirely by putting four kilowatt-hours in a single case.
Caveat the cycle numbers honestly. Budget cells vary more than premium ones, and a 2,000 cycle figure on a $144 battery is an estimate rather than a warranty. Cycle life also depends on how hard you work the pack: shallow daily cycling in mild temperatures beats the rated figure, and repeated full discharges at high current in heat will not reach it. Treat the column as an order of magnitude, not a promise.
Why does charge acceptance matter more than capacity?
Because in a vehicle you are almost never charging for as long as you would like. The alternator runs while you drive, and the sun is useful for four or five hours a day. What determines whether you start tomorrow full is how much energy the battery will physically take in during that window, and this is where AGM quietly loses most of its remaining case.
| State of charge | LiFePO4 accepts, A | AGM accepts, A | LiFePO4 behaviour | AGM behaviour |
|---|---|---|---|---|
| 15 to 50% | 50 | 28 | Flat acceptance, limited only by the charger | Bulk stage, roughly 0.28C |
| 50 to 70% | 50 | 25 | Still flat | Still bulk, beginning to ease |
| 70 to 80% | 50 | 18 | Still flat | Absorption begins, current falls |
| 80 to 90% | 48 | 9 | Very slight taper near the top | Acceptance has collapsed to a third |
| 90 to 95% | 40 | 5 | BMS balancing begins | Hours of charging for very little energy |
| 95 to 100% | 25 | 3 | Short absorption | The long tail nobody waits out in a vehicle |
Follow a two hour drive through that table with a 50A DC-DC charger feeding each battery from half charge. The lithium pack takes 50A for the whole two hours and gains roughly 100 amp-hours, which is more than its remaining space, so it finishes full with time to spare. The AGM takes about 25A for the first hour and about 12A for the second, gaining roughly 37 amp-hours, and it is still not full. It will still not be full after four hours, because the last 20 percent is governed by chemistry rather than by the size of the charger.
The same problem eats solar. An array that produces 30A at midday hands all of it to a lithium bank and only a fraction of it to an AGM bank that has crept above 80 percent, so the controller spends the best hours of the day throttled by the battery rather than by the sun. This is why people with lead banks describe their solar as underperforming when the array is fine. It is also why the answer to a slow-charging AGM system is not a bigger array. Set the chemistry profile correctly on a Victron SmartSolar MPPT 100/30 Solar Charge Controller (Bluetooth) and you will see the taper for yourself in the charge history.
What happens to each chemistry in the cold?
This is the one section where AGM comes out ahead, and it deserves to be stated without hedging. LiFePO4 cells cannot safely accept charge below about 0C. Doing it plates metallic lithium onto the anode, which is permanent capacity loss and a genuine safety issue, so a competent battery management system will simply refuse to charge. The battery still discharges happily in the cold. It just will not refill.
In practice that means a winter trip with a plain lithium pack is a battery that drains and never recovers, which is the worst possible failure mode because it looks fine on day one. The fix is a self-heating pack such as the Renogy 12V 100Ah Self-Heating LiFePO4 Battery (DuoHeat, Mini) , where the heating element draws from the incoming charge source rather than from stored capacity, so the cold costs you charging time instead of usable energy. The Litime self-heating 100Ah and the Renogy 200Ah Pro do the same thing at larger sizes.
AGM will accept charge below freezing, at a reduced rate and with a temperature-compensated voltage, which is a real advantage for a vehicle stored outside through a cold winter. The important counterweight: a lead acid battery that is left discharged in the cold can freeze and crack the case, so the advantage only holds if the bank is kept charged. The winter camping power guide covers how to plan around both behaviours.
What about venting, self-discharge and storage?
AGM is a valve-regulated recombinant design, so under normal charging it recombines the gas internally and vents very little. Under overcharge or a fault it will vent hydrogen, which is why an AGM bank belongs somewhere that can breathe rather than sealed inside a cabinet with no path to outside air. LiFePO4 does not off-gas hydrogen in normal use, which is one reason it has taken over interior installations in vehicles.
Self-discharge favours lithium too, at roughly 1 to 3 percent a month against 3 to 5 percent for AGM. Over a five month off-season that is the difference between a pack sitting at 90 percent and a lead bank sitting near 80 percent, which for AGM is already inside the range where sulphation starts. Lead acid wants to be stored full and topped up; lithium prefers to be stored at around 50 to 60 percent and largely left alone.
One more practical difference: a lithium pack with an internal management system will disconnect itself to protect the cells, at low voltage, at high temperature and at freezing. That is protective and occasionally surprising, because the battery goes from working to apparently dead with no warning. An AGM bank sags gracefully instead, getting weaker and weaker, which is more forgiving and considerably worse for the battery.
Who should choose each chemistry?
Choose LiFePO4 if the vehicle gets used more than a handful of times a year, if weight is anywhere near a constraint, if you charge mainly from an alternator or solar and therefore care about charge acceptance, if the battery lives inside the living space, or if you intend to keep the build for more than about three years. That is most builds, which is why this page has a clear verdict rather than a balanced one.
Choose AGM if the vehicle is stored unheated through a freezing winter and a self-heating lithium pack does not fit the budget, if the build is used four or five nights a year so no battery will ever approach its cycle life, or if you need a cheap bank to absorb a very high momentary discharge such as a winch pull. There is also a legitimate case for keeping an existing healthy AGM in service rather than throwing it away: the greenest battery is the one already in the tray.
Who should not buy the expensive lithium option: if you camp occasionally and your load is lights and phone charging, a 200Ah self-heating pack at $809.99 is several times more battery than you will ever discharge, and the money buys nothing you can use. Size the bank from measured consumption in the battery bank calculator first. Equally, do not buy the cheapest lithium available for a four-season build in a cold climate, because a pack without self-heating in a freezing vehicle is a battery you cannot recharge.
Lithium packs worth considering
Lithova 12V 100Ah LiFePO4 Battery (Group 24, 100A BMS)
The cheapest way into lithium that still ships a 100A BMS and a standard Group 24 case. Budget cells vary more than premium ones, so treat the cycle-life claim as optimistic and the price as the point.
Best for: A first lithium battery in a mild climate
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Renogy 12V 100Ah Self-Heating LiFePO4 Battery (DuoHeat, Mini)
Self-heating is not a luxury feature. LiFePO4 cannot safely accept charge below freezing, so without it a winter trip means a battery that discharges but never refills.
Best for: Anyone who camps below freezing, which is most people eventually
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Litime 12V 100Ah LiFePO4 Battery (Group 24)
A well documented mid-tier cell with a consistent BMS spec and a real support channel behind it. Group 24 dimensions drop straight into most existing battery trays.
Best for: Replacing an AGM battery in an existing tray
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Litime 12V 100Ah RV Self-Heating LiFePO4 Battery
The self-heating version of the same cell. The heater draws from the charge source rather than the battery, so it costs you charging time in the cold rather than stored capacity.
Best for: Four-season builds that still fit a single battery
Check pricePrices change often, confirm on Amazon. Products without a direct listing sell mainly through dealers, so those links open a scoped Amazon search. As an Amazon Associate we earn from qualifying purchases.
What has to change in the build when you switch to lithium?
Four things, and none of them is optional. First, the charge profile. LiFePO4 wants an absorption voltage around 14.2 to 14.6V depending on the manufacturer and effectively no float stage, and running it on an AGM profile with a long float is a slow way to stress the pack. Set the chemistry on the solar controller and the DC-DC charger before the first charge and confirm the figure against the battery datasheet rather than a forum post.
Second, the monitoring. Voltage is a usable fuel gauge on lead acid and close to useless on lithium, because the entire usable range spans about half a volt and load or charge shifts it further. A shunt-based monitor counting amp-hours in and out is the only honest reading, and it is the cheapest component that changes how the system gets used.
Third, the charge source itself. A lithium pack will accept far more current than a lead bank, so an alternator connection that was adequate for AGM can become a heat problem for the alternator when a hungry lithium pack asks for everything it has. A DC-DC charger between the two batteries fixes that by limiting current to a set figure, and it is the reason a DC-DC charger is effectively mandatory on a lithium house bank.
Fourth, the mechanical install does not get easier just because the battery is lighter. A NOCO BT31S Group 31 Heavy Duty Battery Tray and Hold Down and a strap are still the least negotiable fourteen dollars in the build, terminals still get torqued to specification and rechecked after the first trip, and the negative cable is still sized exactly like the positive because it carries the same current.
Where to go next
- The battery chemistry comparison chart, with resting voltages and usable capacity side by side.
- How to size a battery bank, which turns a daily consumption figure into an amp-hour target.
- The winter camping power guide, if freezing charge temperatures are part of your year.
- The lithium battery roundup, for the specific packs worth buying.
- Solar versus alternator charging, which is where charge acceptance turns into real amp-hours.
- LiTime 12V 100Ah RV self-heating LiFePO4 review, the single-product review.
- LiTime 12V 320Ah Mini LiFePO4 review, the single-product review.
Frequently asked questions
Is a 100Ah lithium battery really the same as a 200Ah AGM?
Close enough that the comparison is fair. A 100Ah LiFePO4 pack gives about 85 usable amp-hours at an 85 percent depth of discharge, and a 200Ah AGM gives about 100 usable at 50 percent. So the lithium pack delivers roughly 85 percent of the usable capacity of a bank that weighs three to four times as much, occupies two battery trays and takes far longer to recharge from any source.
Why does AGM charge so slowly near the top?
Lead acid chemistry has rising internal resistance as the plates approach full, so the battery physically cannot absorb current at the same rate. A 100Ah AGM accepting 28A at half charge is down to under 10A by 85 percent and under 5A above 90 percent. The last 20 percent can take three to five hours regardless of how large your charge source is, which wastes both alternator time and afternoon sun.
Can I charge lithium in freezing weather?
Not without a heater. LiFePO4 cells suffer lithium plating if charged below about 0C, which is permanent damage rather than a temporary reduction, so a decent battery management system simply refuses the charge. The fix is a self-heating pack, which draws heater power from the charge source rather than from stored capacity, or a compartment kept above freezing. Discharging in the cold is fine, only charging is blocked.
When is AGM still the right answer?
Three cases. A vehicle stored unheated all winter where a self-heating pack is not in the budget, since AGM accepts charge below freezing at a reduced rate. A build used four or five nights a year, where cycle life will never be reached and the upfront saving is real. And a bank that must survive a very high momentary discharge such as a winch, where a large lead bank is still a robust and cheap answer.
Does lithium need a different charge profile?
Yes, and using an AGM profile on lithium is a common and avoidable mistake. LiFePO4 wants a bulk and absorption voltage around 14.2 to 14.6V depending on the manufacturer, and it wants no float stage at all, or a low float, because holding a lithium pack at absorption voltage indefinitely is stressful. Set the chemistry profile on the solar controller and the DC-DC charger before the first charge, not afterwards.
Do I need a battery monitor with lithium?
Effectively yes. A 12V LiFePO4 pack sits near 13.4V when full and about 12.8V at 10 percent remaining, so the entire usable range spans roughly half a volt, and any load or charge shifts it further than that. A shunt that counts amp-hours in and out is the only honest reading. AGM spans nearly a full volt across the same range, which is why voltage guessing survived as a habit on lead acid.
Electrical safety: 12V is low voltage but not low energy. A lithium house battery can push several hundred amps into a short circuit, and undersized or unfused cable is one of the most common causes of vehicle fires in DIY builds. Every circuit must be fused at the source of power, within a few inches of the battery terminal, at or below the ampacity of the smallest conductor it protects. Size cable for voltage drop as well as ampacity, torque terminals to specification, and have a lithium installation inspected by a qualified installer before it carries load. The figures on this page are researched guidance, not a substitute for ABYC E-11 or your component manufacturer's installation manual.
How we choose: we compare published manufacturer specifications, standards documents including ABYC E-11, and verified owner reviews. We do not test gear in person. Vehicle payload, roof load and charging limits vary by model and year, so confirm yours against the door jamb sticker and the owner's manual rather than any number published here.
Totalling your own build weight against your payload? The Overland Build & Power Planner is the paid version of these pages: 8 printable worksheets you fill in with your own numbers, plus the full PDF, $29.