Every battery comparison in this category is a comparison of sticker prices, and sticker price is close to useless.
A battery is not a thing you buy. It is a quantity of energy you buy, delivered in instalments, and the correct unit of comparison is dollars per usable kilowatt-hour delivered over the battery’s life. Run the numbers that way and the ranking changes sharply — including one result that contradicts what almost every RV dealer will tell you.
The short version: AGM, the default upgrade sold to most owners, is the worst value in the category by a wide margin. Quality flooded lead-acid is far better than its reputation. And the gap between budget and premium lithium is narrower than either camp claims.
Here is the arithmetic, and then the four things it does not capture.
The metric
Cost per usable kWh = purchase price ÷ (usable capacity in kWh × rated cycles at that depth of discharge)Two variables in that equation get misrepresented constantly.
Usable capacity is not nameplate capacity. A 100Ah battery does not give you 100Ah. Lead-acid chemistries are conventionally worked to 50% depth of discharge, because taking them deeper collapses cycle life. Lithium iron phosphate is comfortably worked to 80%, and many manufacturers rate to 100% with a modest cycle penalty. So a 100Ah AGM gives you around 0.6 kWh per cycle and a 100Ah LiFePO4 gives you around 1.02 kWh — before either has delivered a single cycle.
Cycles must be quoted at the same depth of discharge. A cycle to 50% and a cycle to 80% are not the same transaction. Any comparison that puts “700 cycles” next to “5,000 cycles” without stating the depth of discharge, the temperature and the end-of-life threshold is not a comparison at all.
The four contenders
| Flooded lead-acid (golf cart) | AGM | Budget LiFePO4 | Premium LiFePO4 | |
|---|---|---|---|---|
| Typical config | 2 × 6V 225Ah in series | 12V 100Ah | 12V 100Ah | 12V 100Ah |
| Price, Aug 2026 | $380–$450 per pair | $200–$260 | $230–$330 | $650–$900 |
| Usual working DoD | 50% | 50% | 80% | 80% |
| Usable energy per cycle | ~1.35 kWh | ~0.60 kWh | ~1.02 kWh | ~1.02 kWh |
| Rated cycles at that DoD | 1,000–1,200 | 500–700 | 2,000–3,000 | 3,500–5,000 |
| Weight | ~124 lbs | 62–66 lbs | 24–31 lbs | 26–31 lbs |
| Round-trip efficiency | 80–85% | 80–85% | 95–98% | 95–99% |
| Charge below freezing | Yes, reduced acceptance | Yes, reduced acceptance | No, unless heated | No, unless heated |
| Maintenance | Watering, equalisation, venting | None | None | None |
| Typical warranty | 1–2 years | 1–2 years | 3–5 years | 8–10 years |
Cost per usable kilowatt-hour
Multiply usable energy per cycle by rated cycles, divide the purchase price by the result.
| Chemistry | Lifetime energy delivered | Cost per usable kWh |
|---|---|---|
| Budget LiFePO4 | 2,050–3,070 kWh | $0.08–$0.16 |
| Premium LiFePO4 | 3,570–5,120 kWh | $0.13–$0.25 |
| Flooded lead-acid, golf cart | 1,350–1,620 kWh | $0.23–$0.33 |
| AGM | 300–420 kWh | $0.48–$0.87 |
The spread is roughly six to one between the best and worst options, on identical duty.
Two findings are worth sitting with.
Quality flooded lead-acid is genuinely competitive with premium lithium. A pair of 6V golf-cart batteries is a serious deep-cycle product with thick plates, and priced per delivered kilowatt-hour it lands in the same neighbourhood as the expensive lithium brands. The off-grid forums that keep insisting on golf-cart batteries are not simply being stubborn. They are looking at this number.
AGM is not close. It costs roughly what a budget lithium battery costs, delivers 40% less energy per cycle, and lasts a quarter as many cycles. It is the default recommendation at almost every dealership because it is the drop-in replacement that requires no charger changes and no conversation. On cost per delivered kilowatt-hour, it is between three and eight times more expensive than lithium.
Why AGM keeps getting recommended anyway
AGM’s advantages are real, they are just not economic.
It is sealed, so it can be mounted in an enclosed compartment without venting. It is maintenance-free, so nobody has to check electrolyte levels. It tolerates vibration well. It will charge in freezing conditions. And critically, it works with the converter/charger already fitted to the vehicle, which means the sale is a battery rather than a system.
That last point explains most of the market. AGM is what you sell to someone who wants the problem to go away today, and it is a defensible choice for a backup bank that sits on float and cycles a dozen times a year — in that duty, calendar life dominates cycle life and AGM’s poor cycle economics never come into play.
For anything that cycles regularly, it is the expensive option pretending to be the safe one.
Four things cost-per-cycle doesn’t capture
Charging efficiency, which shows up as array size
Lead-acid chemistries return roughly 80–85% of the energy put into them. LiFePO4 returns 95–98%. On mains power that is a rounding error. On solar it is not: the same daily consumption requires meaningfully more array behind a lead bank to arrive at the same net stored energy, and array is the thing you are least able to add later once the roof is full.
The absorption problem, which quietly voids the cycle rating
This is the important one, and it is where the flooded-lead numbers above start to look optimistic in a solar application specifically.
Lead-acid batteries charge quickly to about 80% state of charge, then enter an absorption stage in which the battery’s own chemistry limits how fast it will accept current. That stage takes hours at a tapering rate. It is not the charge controller throttling anything — it is diffusion inside the cell, and no amount of extra panel wattage speeds it up.
The consequence in a solar system is that the sun frequently goes down before absorption completes. The bank never reaches a true 100%, sulfation accumulates, and capacity falls away far faster than the datasheet suggests. Published cycle ratings assume a full recharge every cycle. Chronic partial-state-of-charge cycling is the single most common reason lead banks die years early, and it is a structural feature of solar charging rather than an installation error.
LiFePO4 charges near-linearly to about 95% and takes whatever current is on offer. For solar duty, the battery is essentially never the bottleneck.
Peukert, which shrinks usable capacity under load
Lead-acid capacity ratings assume a slow discharge, conventionally over 20 hours. Pull harder and the available capacity falls. A typical AGM rated at 100Ah over 20 hours delivers around 95Ah over 10 hours and roughly 65Ah over one hour — a 35% loss at high current.
That matters the moment an inverter is involved. Running a microwave or an induction hob pulls at exactly the rate where lead-acid gives up capacity, and the sag in terminal voltage under that load can trip an inverter’s low-voltage cutoff while the battery monitor still reports charge remaining. LiFePO4 exhibits almost no Peukert effect and holds voltage nearly flat across the discharge curve.
Weight, which is really a payload problem
The weight difference reads as a convenience issue and is in fact a compliance one.
Matching the usable capacity of a single 100Ah lithium battery takes roughly two 100Ah AGMs — around 128 lbs against 28 lbs. Scale that to a full-time bank and the difference becomes serious: a lithium bank delivering 4 kWh of usable energy weighs about 120 lbs, while the AGM equivalent is closer to 450 lbs, sited wherever the battery compartment happens to be rather than where the weight distribution wants it.
Most trailers and campers leave the factory with a few hundred pounds of payload margin, and it gets consumed quickly by water, gear and passengers. Adding a quarter of a ton of lead to a rig already near its gross vehicle weight rating is not a theoretical problem — it affects tyre loading, braking and, if it comes to an insurance claim, whether the vehicle was legally loaded at the time. On any weight-constrained platform, the payload arithmetic often decides the chemistry before the cost arithmetic gets a hearing.
Stack these four together and the practical gap between lead and lithium is wider than the cost-per-kWh table alone suggests — particularly for solar-charged systems with substantial inverter loads.
Replacement is not like-for-like
One consequence of the usable-capacity difference gets missed constantly: you should not replace a lead bank with the same nameplate capacity in lithium.
A 200Ah AGM bank delivers about 1.2 kWh per cycle. A 100Ah lithium battery delivers about 1.02 kWh. Replacing 200Ah of AGM with 200Ah of lithium is not a like-for-like swap — it is very nearly a doubling of usable capacity, at a price premium that would not have been necessary.
Work the replacement in usable kilowatt-hours instead. Establish what the old bank actually delivered, decide whether that was enough, and buy that number in lithium. For a great many owners the honest answer is that a single 100Ah lithium battery replaces a pair of AGMs with capacity to spare, which changes the cost comparison considerably — and makes the retrofit cheaper than the headline prices imply. The same logic applies in reverse when sizing a bank for shoulder-season conditions, where the requirement is set by consecutive low-harvest days rather than by whatever was fitted previously.
About those cycle-life claims
Listings advertising 15,000 cycles are not making a claim about your battery.
Cycle ratings are laboratory figures produced under controlled conditions, and the conditions do most of the work. Change the depth of discharge, the charge and discharge rate, the ambient temperature or the end-of-life definition, and the number moves by an order of magnitude. A cell tested at 25°C, at a gentle 0.2C, to 50% depth of discharge, with end of life defined as 70% remaining capacity, will produce a spectacular number that has no bearing on a battery cycled to 80% in a hot roof locker.
Two sanity checks are worth more than the headline figure.
Read the warranty, not the marketing. A manufacturer offering ten years is exposed to its own claims. One offering two years is not, whatever the listing says about 15,000 cycles. The warranty term is the only cycle-life claim the seller has to pay for.
Watch the price floor. LiFePO4 prices rose across 2026 on raw material costs, tariffs and storage demand, after several years of steep declines. Cells did not get cheaper to make during that period. A 12V 100Ah battery listed well below the prevailing market is telling you something about cell grade, BMS quality or both — B-grade cells are commonly 20–30% cheaper and the performance difference is not proportionate.
When lead-acid is still the right answer
The panels-first, lithium-first consensus has genuine exceptions.
Sustained sub-freezing use. LiFePO4 cannot be charged below roughly 32°F without damage. Self-heating models and heated enclosures solve this, at a cost in money and parasitic draw. Lead-acid simply accepts charge at reduced efficiency and gets on with it. If the system will spend winter unheated and charging, the calculation genuinely changes — the failure modes and workarounds for lithium below freezing are worth reading before committing either way.
Low cycle counts. A backup bank that cycles twenty times a year will reach calendar end-of-life long before cycle end-of-life. Lithium’s advantage is in cycles, and if you are not using them you are not buying anything.
Existing charging infrastructure with no budget to change it. A lithium drop-in fitted behind a lead-acid converter/charger will be chronically undercharged, and a lead-acid absorption profile applied to LiFePO4 causes real stress. Doing it properly means new charging hardware, which is the point below.
High cranking current. Starting duty is not deep-cycle duty. Lead-acid remains the sensible chemistry for engine starting.
The retrofit cost nobody includes
Comparing battery prices in isolation understates a lithium conversion, sometimes badly.
Done properly, replacing lead with lithium in an existing rig usually also means a converter/charger with a lithium profile, a DC-DC charger to protect the alternator, upgraded cabling to handle higher charge currents, and often a new charge controller. Those parts routinely add several hundred to a couple of thousand dollars on top of the batteries, and they are the reason so many “cheap” lithium upgrades underperform — the battery was fine, the charging system around it was not. The full costed walkthrough of a lithium retrofit itemises the parts that get left out of the estimate.
It is also worth putting battery replacement where it belongs in the wider ownership picture. Batteries are not a one-time purchase; they are a recurring line item, and over a five-year horizon the chemistry decision is worth more than most of the options people agonise over at purchase. The itemised five-year cost of RV ownership puts the numbers alongside depreciation, insurance and storage, which is the only context in which a battery decision can really be judged.
Frequently asked questions
Is LiFePO4 worth it over AGM? For anything that cycles regularly, yes, and not marginally. Budget lithium delivers three to eight times more energy per dollar over its life, weighs less than half as much, and does not lose capacity under high loads. The exceptions are sustained freezing use and very low cycle counts.
How many cycles does an AGM battery actually get? Quality units are commonly rated at 500–700 cycles at 50% depth of discharge, with premium brands claiming more. Real-world figures are usually lower in solar applications, because chronic incomplete recharging shortens life independently of cycle count.
Can I just drop lithium into my existing RV? Physically, usually. Electrically, not without checking. The converter/charger, alternator charging path and charge controller all need lithium-appropriate profiles. A drop-in behind lead-acid charging hardware will be chronically undercharged and will not deliver the cycle life you paid for.
Are golf-cart batteries still a good option? On cost per delivered kilowatt-hour, yes — they are competitive with premium lithium. The trade-offs are weight (around 124 lbs for a 12V pair), height, the need for venting, watering and periodic equalisation, and vulnerability to the incomplete-recharge problem in solar systems.
What does depth of discharge actually mean for lifespan? Deeper cycles mean fewer of them, but not proportionately. Manufacturer data frequently shows total lifetime energy throughput staying roughly flat or improving slightly as depth of discharge increases, because although you get fewer cycles, each one delivers more. The 50% rule for lead-acid is about avoiding damage at the extreme, not about maximising throughput.
How should I compare two lithium batteries at very different prices? Compare warranty length, stated cycle life at a specified depth of discharge, BMS current rating, and whether the cells are Grade A. Then check whether the cheaper unit’s cycle claim is quoted at the same depth of discharge as the expensive one. Frequently it is not.