LiFePO4 vs Lead-Acid Runtime Compared

A 100Ah LiFePO4 battery can be run much deeper than a 100Ah lead-acid battery. This guide runs LiFePO4 to 80% depth of discharge, where Victron prints a cycle life of 2,500 cycles for its LiFePO4 batteries, and lead-acid to 50%, where Victron prints 600 cycles for its AGM batteries. Same label, very different runtime. This single fact reshapes every comparison between the two chemistries.

This guide puts real numbers behind the LiFePO4 vs lead-acid debate. Not marketing claims: actual runtime, cycle life, and cost-per-kWh figures that help you decide which battery makes sense for your application and budget.

The Runtime Gap at a Glance

The runtime difference is large: on the table's 100W load, LiFePO4 runs about 1.8 to 2.3 times as long as lead-acid (9.2 ÷ 5.0 and 11.5 ÷ 5.0 hours). A LiFePO4 battery at 80% depth of discharge (DoD) delivers more usable energy than a lead-acid battery at 50% DoD, despite both being labeled "100Ah." Run the comparison yourself with our LiFePO4 runtime calculator and lead-acid runtime calculator.

Why LiFePO4 Delivers More Usable Energy

Three factors combine to give LiFePO4 its runtime advantage: deeper safe discharge, flatter voltage curve, and higher round-trip efficiency.

Deeper safe discharge

Deep discharge costs lead-acid batteries cycle life: Victron rates its AGM batteries for 600 cycles at 50% depth of discharge and 400 cycles at 80%. The lead sulfate crystals that form during discharge become hard and irreversible if the battery sits in a deeply discharged state. This is not a theoretical concern: it is the primary cause of premature lead-acid battery failure.

LiFePO4 handles deep discharge far better: Victron rates its LiFePO4 batteries for 2,500 cycles at 80% depth of discharge, and prints a capacity loss of under 1% per 100 cycles at 100% depth. The lithium iron phosphate chemistry does not suffer from sulfation or memory effects. A built-in Battery Management System (BMS) prevents over-discharge by cutting off output before the cells reach a damaging voltage.

Flat voltage curve

Trojan's table for a 12V lead-acid battery prints an open-circuit voltage of 12.73V at full charge and 12.10V at 50% charge, and the voltage keeps falling as the battery discharges. Under load it sits lower still. This sag means your inverter receives progressively less voltage, which increases current draw and reduces overall efficiency.

LiFePO4 voltage stays nearly flat through most of its discharge. Renogy's 12V LiFePO4 voltage chart prints 13.3V at 80% charge, 13.2V at 70% and 12.8V at 20%, a drop of only 0.5V from 80% to 20%. This means steady power delivery: your devices see almost the same voltage at 20% remaining as they did at 80% remaining.

Higher charge efficiency

Victron prints the round-trip energy efficiency of the average lead-acid battery at 80% and of a LiFePO4 battery at 92%. Put an example 1,200Wh into each and you get 1,200 × 0.80 = 960Wh back from the lead-acid battery and 1,200 × 0.92 = 1,104Wh from the LiFePO4. Victron adds that lead-acid charging becomes particularly inefficient once the battery passes 80% state of charge. In solar applications where every watt-hour of panel output counts, this efficiency gap means LiFePO4 banks waste less of your solar harvest.

Real-World Runtime Scenarios

Lab specs are useful, but real applications are what matter. Here are three common scenarios comparing a single 100Ah 12V battery of each type.

Scenario 1: Running a 12V DC fridge overnight

This example assumes a 12V compressor fridge that averages 45W over a 12-hour night as its compressor cycles on and off. Your own fridge's label or manual gives its real figure. Wired straight to 12V with no inverter (100% system efficiency in the runtime calculators):

LiFePO4 at 80% DoD: 100Ah at the 12.8V nominal is 1,280Wh, so 1,024Wh usable; at 45W the LiFePO4 runtime calculator gives 22.8 hours. Easily handles the night with capacity to spare.

Flooded lead-acid at 50% DoD: 600Wh usable, and 13.6 hours at 45W in the lead-acid runtime calculator, which adjusts for the slow 3.75A draw (45W ÷ 12V). Covers the night, but you wake up with a battery that needs immediate recharging to avoid sulfation damage.

Run your own fridge scenario with the 12V battery refrigerator calculator.

Scenario 2: Powering a CPAP machine for camping

CPAP draw depends on pressure settings and humidifier use, so check your own machine's figures. This example assumes the CPAP averages 45W with its humidifier on, runs through an inverter at 90% efficiency, and covers an 8-hour sleep:

LiFePO4 at 80% DoD: 1,024Wh usable, 20.5 hours. Two full nights on one charge, with part of a third.

Flooded lead-acid at 50% DoD: 600Wh usable, 12.2 hours. One full night and about half of a second, but the lead-acid battery is far heavier: RELiON prints 26.4 lbs for its RB100 12V 100Ah LiFePO4, while Victron prints 32 kg (about 71 lbs) for its 12V 110Ah AGM. For backpack camping, weight matters as much as runtime. Dial in exact runtime for your machine with the CPAP battery runtime calculator.

Scenario 3: Home UPS backup during a power outage

This example assumes a basic home office setup (monitor, laptop, router, modem) drawing 150W in total through an inverter at 90% efficiency:

LiFePO4 at 80% DoD: 1,024Wh usable, 6.1 hours. That covers an outage of up to that length at this load; a longer outage needs more capacity or a smaller load.

Flooded lead-acid at 50% DoD: 600Wh usable, 3.0 hours. The inverter loss and the faster draw of about 13.9A from the battery (150W ÷ 0.9 ÷ 12V) both cut into it. Tight for a long outage.

Cost Per Cycle: The Long-Term Math

At this table's example prices, a LiFePO4 battery costs about 2.5 times as much upfront as a lead-acid battery with the same rating. But upfront cost is not the right metric: cost per usable kWh over the battery's lifetime is.

At these example prices, LiFePO4 delivers each kilowatt-hour for about a third of what lead-acid costs over its life: $0.14 against $0.39 at the middle of each price range. Daily cycling makes the gap plain. Cycled once a day to 50% depth, Victron's AGM rating of 600 cycles lasts about 20 months. The same daily 50% cycling reaches Victron's LiFePO4 rating of 5,000 cycles at 50% depth in about 13.7 years. Over a decade of daily cycles (3,650), that is about six AGM batteries for one LiFePO4, counting cycles alone. To compare these economics against your grid electricity rate, check the cost per kWh calculator.

The exception: if you need batteries for a system that cycles only occasionally, such as a boat used on some weekends or a cabin visited monthly, lead-acid's lower upfront cost can make financial sense because you'll never reach the cycle count where LiFePO4's longevity advantage kicks in.

Voltage Under Load: The Hidden Runtime Advantage

Runtime calculations assume constant voltage, but lead-acid batteries do not deliver constant voltage. A 12V lead-acid battery's voltage falls steadily as it discharges, and it sits lower still while a load is drawing current. This voltage sag forces your inverter to draw more current to maintain output power (P = V × I, so as voltage drops, current must rise to keep watts constant).

Higher current draw means higher losses in wiring, connectors, and the inverter itself. Take a 1,000W draw on the battery at two example voltages: at 1,000W and 11.8V the solar watts to amps calculator gives 84.75A, and at 1,000W and 13.0V it gives 76.92A. That is about 9.2% less current ((84.75 - 76.92) ÷ 84.75), and less current means lower I²R wiring losses and less heat throughout the system.

This effect compounds with larger loads. If you are sizing cables for an inverter system, the lower voltage of lead-acid under load means you need thicker cables to avoid excessive voltage drop, a hidden cost that rarely shows up in battery comparison articles. Size your cables correctly with the inverter cable sizing calculator.

Charging Infrastructure: What Each Chemistry Demands

The battery itself is only part of the system cost. Charging infrastructure differs between the two chemistries in ways that affect both performance and total investment. To turn the maker's printed charge limits into a charger rating for your own bank, see our guide to sizing a battery charger.

Charger compatibility. Lead-acid batteries use a well-established three-stage charging profile (bulk, absorption, float). LiFePO4 requires a different profile: higher bulk current acceptance and a lower charge voltage. Victron prints a charge voltage of 14.0-14.4V (14.2V recommended) and a float of 13.5V for its LiFePO4 batteries, against an absorption voltage of 14.2-14.6V for its AGM batteries in normal cycle service.

Some smart chargers and MPPT charge controllers include a LiFePO4 mode, and some converters and chargers offer only lead-acid profiles: the charger's manual says which it has. Replacing a converter with one that has a LiFePO4 setting is an extra cost to budget for.

Solar charge rate. LiFePO4 batteries accept charge current much faster than lead-acid. For its LFP-Smart 12,8/100, the 12.8V 100Ah model, Victron's datasheet prints a recommended charge current of 50A (50A ÷ 100Ah = 0.5C) and a maximum charge current of 200A. Lead-acid makers print lower limits. In its answers on VRLA (gel and AGM) batteries, East Penn advises using the highest initial charging current available, "up to 30% of the 20-hour capacity per hour": for a battery rated 100Ah at the 20-hour rate, 30% is 30A. Victron says the charge current for its gel and AGM batteries should preferably not exceed 0.2C, which is 20A for a 100Ah battery. The 100Ah battery charge time calculator takes the charge current, the depth of discharge and the chemistry, and returns the charge time in hours with its bulk and absorption stages.

In a solar system, this means a LiFePO4 bank can take in a strong midday harvest close to the rate the panels produce it, while a lead-acid bank limits the current and needs more hours to absorb the same energy. On partly cloudy days with short windows of strong sun, that difference shows up as more energy stored.

Alternator charging. For marine and RV applications, alternator charging while the engine runs is a major energy source. LiFePO4's high charge acceptance means a DC-DC charger can run at its full rated current into the house battery during a drive. Lead-acid accepts less current and takes longer to reach full charge because of the extended absorption phase, so the same drive puts back less of a lead-acid bank of the same size.

Temperature restrictions. LiFePO4 batteries carry a printed low-temperature limit for charging. Victron prints a charge range of +5°C to +50°C (41°F to 122°F) for its LiFePO4 batteries, and RELiON prints a maximum charge current of 0.1C (10A) for its RB100 12V 100Ah battery between 14°F and 32°F (-10°C to 0°C). Lead-acid charges slowly in cold weather but has no hard cutoff. For winter marine or RV use, some LiFePO4 batteries include internal heaters that warm the cells above the charge threshold automatically, which adds to the battery's price. This cold-weather limitation is one reason engine starting still relies on lead-acid batteries and their cold cranking amps rating rather than lithium. The solar battery charge time calculator takes the battery capacity, the solar wattage, the peak sun hours, the system voltage, the chemistry, the depth of discharge, the system losses and the battery charge efficiency, and returns the charge time in days, the daily solar energy and the energy to replenish. For a boat that runs its season off a deep-cycle house bank, the boat battery runtime tool takes the chemistry and the depth limit you actually stop at.

Which Battery Should You Choose?

LiFePO4 wins on runtime, weight, cycle life, efficiency, and lifetime cost. Lead-acid wins on upfront price and availability. The choice depends on your application.

Choose LiFePO4 if: you cycle the battery daily (solar, RV, van life), weight matters (boats, portable systems), you want the battery to last through many years of daily cycles, or you need maximum runtime from a given physical space. Our CPAP off-grid guide is a good example of a weight-sensitive application where LiFePO4's advantages are most pronounced.

Choose lead-acid if: the battery cycles infrequently (seasonal cabin, emergency backup only), upfront cost is the primary constraint, or you need batteries immediately and cannot wait for shipping (lead-acid is available at every auto parts store).

Choose AGM (a lead-acid subtype) if: you want maintenance-free lead-acid, need the battery in an enclosed space (no hydrogen venting), or you are upgrading an existing lead-acid system and do not want to change your charging setup.

For a detailed capacity comparison for your specific setup, the deep cycle battery runtime calculator lets you pick the chemistry first, then set the depth of discharge, efficiency and load to see the runtime each chemistry gives.