Introduction: Three technologies – one decision
Whether for your vehicle, motorhome, solar system or marine use – choosing the right battery is an investment in reliability and performance. AGM, GEL and LiFePO4 are the three dominant technologies for 12-volt applications, and each brings specific strengths. This comparison provides you with all the technical facts, real values and honest assessments so that you do not get lost in the datasheet jungle.
All AGM batteries at a glance, with selection aid and table: AGM battery.
What is an AGM battery?
AGM stands for Absorbent Glass Mat. The electrolyte is bound in a glass-fibre mat, which makes the battery leak-proof and vibration-resistant. Nominal voltages of 12 V and capacities from 44 Ah to well over 100 Ah are typical. A 100 Ah model weighs around 25 kg depending on the design and delivers cold cranking currents (CCA EN) of 680 A to 760 A. Thanks to the low internal resistance, AGM is excellently suited to start-stop systems and high current outputs. The cycle life is around 300–500 full cycles at 50 % depth of discharge (DoD). In the partial discharge range, significantly more microcycles are possible. With proper charging – final charging voltage 14.4–14.8 V, float charge 13.5–13.8 V – AGM batteries impress with low maintenance requirements. Further details can be found on our AGM basics page or specifically for cars under AGM car battery.
What is a GEL battery?
In a GEL battery, the liquid electrolyte is thickened into a gel by silica. The screw-fixed valves provide overpressure safety, and internal gas recombination achieves efficiencies of almost 99 %. GEL batteries operate reliably in a temperature range from -30 °C to +60 °C and are extremely resistant to deep discharge. A 12 V GEL battery with 100 Ah weighs around 30–32 kg and can deliver cold cranking currents of 550–650 A (EN). Cycle resistance is 500–800 cycles at 50 % DoD – ideal for cyclic applications such as the motorhome body or off-grid solar island systems. Gel batteries require precise charging behaviour: charging voltage maximum 14.1–14.4 V, thermal monitoring is strongly recommended. Even slight overvoltages can lead to irreversible capacity loss through gel cracks. That is why modern chargers and trickle chargers with temperature compensation are indispensable.
What is a LiFePO4 battery (lithium iron phosphate)?
LiFePO4 is the safest variant of the lithium-ion family. The nominal voltage is 12.8 V, the energy density is around 90–120 Wh/kg. A 100 Ah LiFePO4 battery weighs only 11–13 kg – roughly half that of a comparable AGM model. The cycle life reaches an impressive 2,000–5,000 full cycles at 80 % DoD, and over 7,000 microcycles have been documented for partial discharges. The usable capacity is often over 90 %, while lead batteries (AGM/GEL) age quickly under regular deep discharges. The calendar life advantage: LiFePO4 reaches 10–15 years with minimal capacity loss. The charging technology is different: constant current-constant voltage to 14.2–14.6 V, then switch-off; trickle charging is harmful. The integrated battery management system (BMS) protects against overcharging, deep discharge and short circuit.
Comparison table: technical data at a glance
| Property | AGM | GEL | LiFePO4 |
|---|---|---|---|
| Nominal voltage | 12 V | 12 V | 12,8 V |
| typical capacity (12 V) | 60–120 Ah | 80–200 Ah | 50–300 Ah |
| Cycles (at 50 % DoD*) | approx. 300–500 | approx. 500–800 | 2,500–5,000 (at 80 % DoD) |
| Weight (100 Ah) | approx. 25 kg | approx. 30–32 kg | 11–13 kg |
| Typical cold cranking current (EN) | 680–760 A | 550–650 A | not specified as a starter** |
| Charging efficiency | 70–80 % | 85–90 % | 95–99 % |
| Temperature range | -30 °C to +50 °C | -30 °C to +60 °C | -20 °C to +60 °C (charging >0 °C) |
| Self-discharge/month | 2–3 % | 1–2 % | <1 % |
| Toxicity/environment | Lead, sulphuric acid | Lead, sulphuric acid, gelling agent | Lithium iron phosphate, recyclable |
* DoD = Depth of Discharge
** LiFePO4 can be used as a starter battery with a suitable BMS design, but the CCA values are manufacturer-dependent and not a primary design criterion.
Areas of application: where the strengths lie
AGM – king of start-stop and high-current applications
Anyone who starts, brakes and accelerates every day benefits from the high current output and cycle resistance in microcycles. The 100 Ah AGM is a classic for motorhomes with a fridge and auxiliary heater, while the 80 Ah variant is often used in mid-range cars with start-stop. AGM is also popular as a supply battery in caravans – thanks to vibration resistance and flexible installation position.
GEL – the deep discharger for continuous operation
GEL batteries play to their strengths in cyclic applications with slow, regular discharges: photovoltaic island systems, wheelchairs, cleaning machines or emergency lighting. The excellent cycle resistance under deep discharges makes them the first choice when a mains connection is not permanently available. Anyone looking for a body battery for the motorhome will find a robust solution in GEL technology.
LiFePO4 – the lightweight with maximum service life
Lithium iron phosphate batteries are ideal for mobile systems where every kilo counts: campers, boats, drone stations and portable power stations. The high cycle resistance amortises the higher purchase price under intensive use – for example on daily camping tours or in off-grid solar storage. Thanks to the flat discharge curve and the BMS, deep discharge is safe and powerful.
Charging and maintenance concepts: crucial for service life
The charging algorithms differ fundamentally. AGM and GEL require temperature-dependent IU chargers with end-of-charge voltages that take the acid type into account. A wrong charger can cause irreversible gassing and drying out in a GEL battery after just a few cycles. LiFePO4 requires a specific lithium charging profile with constant current (0.3–1C), constant voltage 14.2–14.6 V and immediate charge cut-off – trickle charging would damage the cells. A precise BMS is integrated, but the charger must be designed for lithium. With the right care – regular voltage checks, correct storage (50 % SoC for LiFePO4, 100 % for lead), clean terminals and temperature protection – you can significantly increase the service life of every type. Particularly important: frost protection measures, as we describe in detail in our guide to frost protection.
Environmental aspects and safety
AGM and GEL contain lead and sulphuric acid, but are 98 % recyclable under the EU Batteries Directive. GEL batteries bind the acid, which minimises leakage risks. LiFePO4 is free from toxic heavy metals, thermally stable and non-flammable. However, recycling requires specialised processes that are still being established. In terms of operational safety, LiFePO4 offers extremely low self-discharge and no oxyhydrogen formation thanks to the BMS and low internal resistance – when installed correctly.
Cost-benefit analysis: total cost of ownership
The pure purchase costs are deceptive. When considered holistically over 10 years, LiFePO4 often comes out cheaper: a 100 Ah LiFePO4 battery with 2,500 cycles delivers around 200,000 Wh of usable energy over its service life (80 % DoD), while an AGM battery with 400 cycles at 50 % DoD reaches only 24,000 Wh. Four AGM batteries would be needed for the same energy, which almost cancels out the cost difference. The individual case decides: anyone who uses the vehicle only seasonally is well served by AGM; with daily cycling, LiFePO4 pays for itself quickly.
Conclusion: which battery type suits you?
The overview shows: AGM is the all-rounder for start-stop and budget-conscious campers, GEL is the specialist for regular deep discharges, and LiFePO4 is the premium battery for maximum cycles and low weight. Determine your actual depth of discharge, the number of cycles required per season and the permissible weight. If in doubt, the Electronicx team from Cleebronn will advise you personally. Call us on +49 7135 7194106 or write to [email protected]. Our company headquarters: Electronicx GmbH, Hindenburgstr. 37A, 74389 Cleebronn, Germany (Amtsgericht Stuttgart HRB 752730, VAT ID No. DE300176428, Managing Director Andreas Emschanow).
Frequently asked questions
Can I charge an AGM battery with a normal charger?
Yes, provided the charger reaches an end-of-charge voltage of 14.4–14.8 V and switches to trickle charging of a maximum of 13.8 V once full charge is reached. Older, unregulated chargers can overcharge and damage the battery.
What happens if I overcharge a GEL battery?
Even voltages above 14.4 V lead to gassing and can cause cracks in the gel electrolyte. This pore formation is irreversible and drastically reduces capacity – a capacity loss of 20 % after a single overcharge is not uncommon.
Is a LiFePO4 battery suitable as a starter battery?
Technically possible if the BMS releases the high current for the starter and the cells deliver corresponding cold cranking currents. However, most LiFePO4 blocks are designed for continuous currents of 100 A – for large diesel engines this can be tight. Always check the manufacturer's specification for maximum pulse current.
Why is the usable capacity higher with LiFePO4?
Unlike lead batteries, which at 50 % DoD can only permanently deliver half their nominal capacity, LiFePO4 allows discharge down to 80 % or even 90 % without any significant loss of service life. Therefore, a 100 Ah LiFePO4 battery actually provides 80–90 Ah.
Which battery lasts longer: AGM or GEL?
GEL usually exceeds AGM in cycle life by 30–50 %. At the same depth of discharge, GEL reaches 500–800 cycles, AGM around 300–500. However, GEL is more sensitive when charging, so AGM can be more robust in everyday automotive use.
Can I charge a LiFePO4 battery outdoors in winter?
Lithium iron phosphate cells must not be charged below 0 °C, as this leads to lithium plating and destroys the cells. Modern BMSs interrupt charging automatically at freezing temperatures. For outdoor use, batteries with integrated heating or installation in a temperature-controlled location are required.
What battery size (Ah) do I need for my motorhome?
This question cannot be answered in general terms. As a rule of thumb: the daily consumption in Ah multiplied by 2 (for AGM) or 1.3 (for LiFePO4) gives the required nominal capacity. A consumption of 40 Ah per day therefore requires an AGM with at least 80 Ah or a LiFePO4 with 50 Ah. Also take charging sources such as solar or alternator into account.