Can I charge an AGM battery with a regular charger?

You need a charger with an AGM or VRLA setting. AGM takes a lower absorption voltage than flooded: Lifeline specifies "14.3 volts ± 0.1 volts" at 77°F (25°C) and Fullriver prints 14.3 to 14.5V for cycle service, against the 14.82V bulk setting Trojan prints for a 12V flooded string. Overcharging an AGM builds internal pressure and can permanently damage the sealed cells, which is why that half-volt matters. Most smart chargers detect AGM or offer it as a mode; if yours does not, match the maker's number instead of guessing at a nearby profile. 14.3V at 25°C is the figure to dial in.

How long does an AGM battery last in a car?

No maker publishes a service life in years for car use, because it depends on how the car treats the battery. What they do print is two figures. Victron gives its 12V Deep Cycle AGM a "float design life: 7-10 years at 20°C", the case where the battery sits charged and barely cycles, which is close to how a starting battery lives. It also prints cycle design life by depth: 1500 cycles at 30%, 600 at 50%, 400 at 80%. A stop-start car cycles the battery shallowly but constantly, so it lands between the two. Heat pulls both numbers down, so a battery in a hot engine bay ages faster than the same battery in a cool boot, and capacity loss shows up first as slow cranking on cold mornings.

Is AGM better than gel for deep cycling?

Gel does last longer per cycle at the same depth, and one datasheet settles it because it prints both: Victron gives its 12V Deep Cycle GEL 500 cycles at 80% discharge, 750 at 50% and 1800 at 30%, against 400, 600 and 1500 for the AGM of the same range. That is roughly a quarter more cycles at every depth. The trade-off runs the other way on cost and on handling: gel costs more, is less forgiving of charging voltage, and Concorde (an AGM maker, so read it with that in mind) reports that the semisolid electrolyte "develops cracks and voids that reduce contact between the plates" in high-temperature use. The Gel row in the comparison above shows the runtime difference at your own load; it is small, because depth and cycle life, not delivered capacity, are where the two chemistries part.

AGM Battery Runtime Calculator - 50% DoD

7 min read

AGM (Absorbed Glass Mat) batteries sit between flooded lead-acid and LiFePO4 in price and in what they will take. They are sealed, spill-proof and hold up to vibration, which is why they end up in boats, RVs and UPS cabinets. This AGM battery runtime calculator estimates how long a bank holds a load, and it applies a discharge-rate correction read off Victron's printed AGM deep-cycle table rather than reading the label amp-hours straight off: a 280W draw and a 60W draw are not the same battery. Lifeline's printed table for its GPL-31T sits 3 to 8 percent below Victron's between the 8 A and 25 A rates; this calculator uses Victron's table across its full range. Many modern vehicles ship with AGM from the factory, so for accessory runtime with the engine off, see our car battery runtime calculator.

AGM battery stats: 50 percent maker depth limit, 600 cycles at that depth, 12.78 volts rested, fully charged (Lifeline).

AGM vs Standard Flooded Lead-Acid

Characteristic	AGM	Flooded Lead-Acid
Internal resistance	Lower: Lifeline puts it down to closer plate spacing, which gives "better power performance on discharge"	Higher, with more voltage sag under the same load
Bulk charge current	Fullriver prints a 25A maximum for its 105Ah DC105-12, 0.24C	US Battery prints bulk charge at about 10% of the 20-hour capacity, 0.1C
Vibration and spillage	Lifeline: electrolyte "remains immobilized even when the battery is exposed to severe vibration"; non-spillable	Lifeline: "Electrolyte spills when battery is tilted, inverted, or cracked"
Self-discharge	1-3% per month (Lifeline)	5-15% per month (Trojan)
Cycle design life	Victron prints 600 cycles at 50% DoD and 400 at 80% for its 12V Deep Cycle AGM; Odyssey prints 400 cycles to 80% DoD	Published as a chart against depth rather than a single figure, so read your own datasheet
Maintenance	None, sealed	Monthly water checks; hydrogen must be vented
Cost per 100Ah	$150-300	$80-150

Prices and rates on this page are our own estimates as of the date shown; they change often. Enter your own figures for a current result. The rest of the table is what the makers themselves publish, and it explains why AGM ends up in vehicles and boats: it takes charge faster, it does not spill, and it holds its charge in storage about five times longer than a flooded battery does.

The runtime above is not the label amp-hours divided by watts. It applies a rate correction read off Victron's printed AGM deep-cycle table, interpolating between the printed rows, so it returns each of those printed points exactly (the same method runs through Trojan's flooded rows and Victron's gel rows). That matters because the makers print the same thing: capacity falls as you pull harder. Victron's own table gives 100% of rated capacity over 20 hours, 92% over 10, 85% over 5 and 78% over 3, and adds that "the capacity reduction will be even faster in case of a constant power load, such as an inverter", which is exactly what the watts box above describes.

AGM battery runtime falling as load rises from 60 to 280 watts on a 100Ah 12V bank. — Doubling the load from 100W to 200W cuts AGM runtime from 5 to 2.3 hours, less than half, because capacity itself falls as the draw rises.

When AGM Makes the Most Sense

AGM batteries excel in applications where three conditions meet: moderate cycling (not daily deep discharge), enclosed installation (no ventilation for hydrogen gas), and vibration or movement (boats, vehicles, portable setups).

Specific scenarios where AGM outperforms alternatives: dual-purpose marine batteries (starting plus trolling), RV house batteries where you cannot maintain flooded cells, UPS backup systems in office environments, and overland vehicle auxiliary batteries mounted under seats or in tight spaces.

Where AGM falls short: daily-cycle solar storage (LiFePO4 wins on cost per cycle) and budget stationary work (flooded wins on upfront cost). Victron prints 400 cycles at 80% discharge for its 12V Deep Cycle AGM, which is about 13 months of daily cycling (400 ÷ 365); holding to 50% stretches its printed 600 cycles to about 20 months. Neither number is a warranty. They are design figures from one maker's datasheet, and heat shortens both.

One AGM advantage that does not show up in the runtime: cold cranking. Lifeline's technical manual puts it down to construction, saying closer plate spacing gives "the AGM battery a lower internal resistance, making it more charge efficient and giving better power performance on discharge", and Lifeline's own blog says AGM carries "a higher cold cranking amps (CCAs) rating than your average battery". Neither prints a percentage, so treat it as a direction rather than a number. It is a large part of why stop-start vehicles ship with AGM.

Worked Examples

AGM vs Flooded for a Marine House Battery

Context

You are choosing a 100Ah house battery for your boat. An AGM costs $280, a flooded costs $150. Both are 12V. Your loads are 80W (fish finder, radio, lights) for 6-hour trips.

Calculation

The 80W load through a 90% efficient inverter draws 80 ÷ 0.90 ÷ 12 = 7.4A, which is 0.074C on a 100Ah battery, inside the range both makers print.

AGM at 50% DoD: 6.4 hours (6 hours 24 minutes).

The same battery as flooded lead-acid, same depth, same inverter: 6.4 hours. There is no gap at this rate, and no difference in stored energy either.

Interpretation

Identical at this load, and that is the honest answer: at 0.074C Victron's printed AGM rows and Trojan's printed flooded rows give the same capacity, because both makers print 100% at the 20-hour rate and 92% at the 10-hour rate. Pull harder and the two part: at 200W the AGM reads 2 hours 15 minutes against 2 hours 8 minutes for flooded, because above the 10-hour rate Victron's AGM rows fall more slowly than Trojan's flooded rows. What you are buying with AGM is zero maintenance, mounting at any angle, vibration tolerance and a self-discharge rate about a fifth of a flooded battery's. On a boat with the battery in a hard-to-reach locker, those decide it.

Takeaway

The difference between the two shows at heavier loads: at 400W the AGM runs 59 minutes against 50 minutes for flooded, though 400W is past the fastest rate Trojan prints for flooded, so that figure extends the printed trend past the data and real runtime may be shorter. If you also need trolling motor power, you will want a separate starting battery. Check your motor's runtime needs with our marine battery runtime calculator.

Will an AGM Battery Handle an RV Inverter?

Context

Your RV has two 100Ah AGM batteries (200Ah parallel) and a 1,000W inverter. Evening loads average 400W for 4 hours.

Calculation

Energy needed: 400 x 4 = 1,600 Wh.

The 400W load draws 37A from the 200Ah bank through a 90% inverter, 0.185C, still inside the printed range. At 50% DoD the calculator returns 2.3 hours (2 hours 15 minutes), so the bank delivers about 902 Wh before it hits that depth.

902 against 1,600 needed: the evening is 698 Wh short.

Interpretation

The AGM bank does not hold 4 hours at 400W; it holds about 2 hours 15 minutes. Note that the identity most calculators use, 200 x 12 x 0.50 = 1,200 Wh minus inverter losses, would have promised you 2.7 hours. The extra 27 minutes is the rate effect this page corrects for, and it is the difference between finishing the evening and tripping the low-voltage cut-out.

Takeaway

A LiFePO4 bank of the same 200Ah, at the 100% depth of discharge Battle Born prints and the 12.8V nominal Victron prints, runs 5 hours 46 minutes on the same load, 2.6 times the AGM figure. Size the bank for your own evening with our RV battery runtime calculator.

Frequently Asked Questions

Glossary

Absorbed Glass Mat

A sealed lead-acid battery where the electrolyte is held in fiberglass mats between the plates. AGM batteries are maintenance-free, spill-proof, mount in any position, and handle vibration better than flooded batteries. They cost roughly twice as much per Ah as flooded, on the prices in the table above.

Self-Discharge Rate

The rate at which a battery loses charge while sitting idle. Flooded lead-acid loses 5-15% per month. Lifeline prints 1-3% per month for its AGM. Battle Born prints 2-3% per month for its LiFePO4. High self-discharge means more frequent maintenance charging.

Gel vs AGM

Both are sealed lead-acid, but gel batteries use silica-thickened electrolyte while AGM uses glass mat separators. AGM handles higher discharge rates and is more common. Gel is more sensitive to overcharging but better at very slow, deep discharges.

Sizing an AGM bank for solar? The solar battery bank size calculator helps you match panels to AGM storage capacity.

AGM is the practical middle ground: more capable than flooded, cheaper than LiFePO4, and sealed, which decides it for a lot of installations on its own. If you cycle daily, the printed cycle counts say LiFePO4 wins on long-term cost. If you cycle rarely and want nothing to maintain, AGM earns its premium. Our LiFePO4 vs lead-acid comparison works through the cost-per-cycle arithmetic. For a bank you cycle hard, the deep cycle runtime calculator runs the same rate-corrected engine with the chemistry as a choice rather than fixed to AGM.

More Battery calculators

Browse all battery calculators: LiFePO4, lead-acid, AGM, and lithium-ion runtime, charge time, and capacity sizing.

Last updated: October 25, 2026

Written and maintained by Dan Dadovic, Commercial Director at Ezoic Inc. & PhD Candidate in Information Sciences. On the energy side, Dan has hands-on experience with residential solar panel installation, DIY battery bank construction, off-grid power systems, wind power, and EV ownership/driving, all from building, maintaining, and operating his own systems.

Disclaimer: Calculator results are estimates based on theoretical formulas. Actual performance varies with temperature, battery age, load patterns, and equipment condition. For critical electrical work, consult a licensed electrician.

Methodology reviewed by Doc. dr. sc. Damir Topić, Assistant Professor, FERIT Osijek.