Battery Types and Deep Cycle: A Data-Backed Guide for Off-Grid Solar

314 battery-equipped solar kits exist in the OffGridEmpire database. Of those, 311 use LiFePO4. Two use AGM. One uses Li-ion. That ratio tells a story the industry has already settled, but most guides never explain why.

Competitor articles publish 350-500 word overviews of battery types and deep cycle technology with zero real specs. No cycle counts. No DoD percentages. No cost per usable Wh. No cold-weather charge limits. This guide provides all four, backed by manufacturer data, real kit pricing, and third-party testing.

What follows covers six battery chemistries and configurations: flooded lead acid, AGM, and LiFePO4 compared across cycle life, round-trip efficiency, self-discharge, weight, charge controller requirements, and lifetime cost per cycle. Every claim references a specific kit from the OGE database -- from the WindyNation 400W Complete Off-Grid Kit AGM system at $1,149 to the ECO-WORTHY 200W 12V Complete Kit LiFePO4 kit at $540 -- or a published manufacturer spec.

Sections are ordered by chemistry (FLA, AGM, LiFePO4), then by the three decisions that follow: lifetime cost per cycle, voltage and charge controller pairing, and use-case matching. Eight FAQ answers close the guide with direct, data-backed responses.

No opinions. No rankings. Numbers only.

What "Deep Cycle" Actually Means

80% of battery failures in off-grid systems trace back to one misunderstanding: depth of discharge. "Deep cycle" does not mean a battery can be fully drained. It means the battery is engineered to deliver a portion of its capacity repeatedly without permanent damage. The defining spec is Depth of Discharge (DoD) -- the percentage of total capacity used before recharging.

Cycle life depends entirely on DoD. Data from Himax Battery on LiFePO4 cells shows the relationship:

• 100% DoD = 600 cycles
• 80% DoD = 900 cycles
• 40% DoD = 3,000 cycles
• 20% DoD = 9,000 cycles

The curve is not linear. Cutting DoD in half more than triples cycle life. This is why manufacturer-rated DoD matters more than nameplate capacity.

The Marine Battery Mistake

A common error is using a marine "starting/deep cycle" hybrid battery for solar. These batteries optimize for high cranking amps, not sustained discharge. Their thin plates degrade rapidly under daily cycling. A true deep cycle battery uses thicker plates designed for repeated partial discharge.

The WindyNation 400W Complete Off-Grid Kit kit uses AGM deep cycle batteries rated for 50% DoD. From 1,200Wh nameplate, that means 600Wh usable per cycle. The ECO-WORTHY 200W 12V Complete Kit kit uses LiFePO4 rated for 80% DoD -- delivering 1,024Wh usable from 1,280Wh nameplate.

Same category. Different usable output by 70%.

Why DoD Matters More Than Capacity

A 200Ah AGM battery at 50% DoD delivers the same usable energy as a 100Ah LiFePO4 battery at 100% DoD. Nameplate Ah printed on the label is not what reaches the load. Usable capacity -- nameplate multiplied by rated DoD -- is the only number that matters for system sizing.

The cross-chemistry DoD comparison reinforces this: AGM at 50%, FLA at 50% optimal, and LiFePO4 at 80-100%. Two chemistries lose half their nameplate capacity to DoD limits. One loses 0-20%. Batteries also degrade through calendar aging -- capacity loss over time regardless of cycling -- but cycle-driven DoD degradation dominates in daily-use off-grid systems.

Every kit comparison on this site uses usable capacity, not nameplate, when calculating cost per Wh. That distinction changes the math on every kit in the database.

Flooded Lead Acid (FLA): The Legacy Chemistry

$80-$120 for a 100Ah FLA battery makes it the lowest upfront option by a wide margin. A comparable Renogy AGM 100Ah costs $189.99. That price gap explains why FLA dominated off-grid systems for decades.

FLA batteries use liquid sulfuric acid electrolyte with lead plates fully submerged. The chemistry is simple and well understood.

FLA Specs

• DoD: 80% possible, 50% optimal
• Cycle life: 300-700 cycles at 50% DoD
• Round-trip efficiency: 70-80% (Fire Mountain Solar)
• Self-discharge: 10-15% per month
• Cost per cycle: $4.59 (Greentech Renewables, 48V system analysis)

That 70-80% efficiency number means 20-30% of every watt harvested by solar panels converts to heat inside the battery. Over a year of daily cycling, that loss compounds.

The Maintenance Reality

FLA batteries require hands-on maintenance per Trojan Battery specifications: check electrolyte levels every 2-4 weeks using a hydrometer, add distilled water only (never tap water), and run equalization charges every 30-90 days at 15.5V (for 12V systems). Target specific gravity post-charge is 1.265, with 1.225 as the minimum before corrective action.

Skip equalization and individual cells drift out of balance, reducing effective capacity. Skip water checks and plates become exposed, causing permanent sulfation. FLA maintenance is not optional -- it is the price of the lower buy-in.

Where FLA Still Works

Seasonal cabins used 30-60 days per year may not reach 300 total cycles within the battery's calendar life. Very large battery banks (over 10kWh) where FLA's lower cost per Ah saves thousands upfront can also make sense -- if the owner performs scheduled maintenance.

The 10-15% monthly self-discharge rate means an FLA bank left idle for 3 months loses 30-45% of its charge. Seasonal users must add a maintenance charger or risk sulfation damage.

No kit in the OGE database ships with FLA batteries. The WindyNation 400W Complete Off-Grid Kit uses AGM, which eliminates FLA's maintenance burden at a higher price point. Zero of 16 brands across 314 battery-equipped kits chose FLA for their products.

FLA is the lowest-cost battery chemistry to buy and the highest-cost to own.

AGM (Absorbed Glass Mat): The Maintenance-Free Compromise

$1,259 real build cost for the WindyNation 400W Complete Off-Grid Kit AGM kit delivers 600Wh usable capacity. The ECO-WORTHY 200W 12V Complete Kit LiFePO4 kit costs $575 real build cost and delivers 1,024Wh usable. That is 70% more usable energy for 54% less money.

AGM batteries suspend their electrolyte in fiberglass mats between lead plates. The design is sealed and spill-proof, requiring no water additions.

AGM Specs

• DoD: 50% maximum recommended
• Cycle life: 300-500 cycles at 50% DoD (quality AGM like Concorde Lifeline reaches 2,050 cycles)
• Round-trip efficiency: 80-85%
• Self-discharge: 3-5% per month
• Cost per cycle: $5.27 (Greentech Renewables) -- the highest of all three chemistries
• Absorption voltage: 14.4-15.0V (BatteryStuff)

Real Kit Comparison

The WindyNation 400W Complete Off-Grid Kit ships with 2x AGM batteries: 1,200Wh total, advertised price $1,149, real build cost $1,259, cost per Wh $1.05/Wh. At 50% DoD, usable capacity is 600Wh. Each AGM battery weighs approximately 60-70 lbs per 100Ah, putting the 300Ah bank near 180-210 lbs total.

The ECO-WORTHY 200W 12V Complete Kit LiFePO4 kit: 1,280Wh total, advertised price $540, real build cost $575, cost per Wh $0.45/Wh. At 80% DoD, usable capacity is 1,024Wh. LiFePO4 at 25-30 lbs per 100Ah cuts that weight by more than half.

AGM also suffers from the Peukert Effect: rated capacity drops under high-current loads. A 100Ah AGM battery drawn at its 1-hour rate delivers approximately 50-60Ah, not 100Ah. LiFePO4 maintains rated capacity regardless of discharge rate.

Where AGM Genuinely Wins

AGM has four legitimate advantages:

1. Cold charging below <data>32°F</data>: LiFePO4 BMS locks out charging below freezing (LiTime data). AGM charges normally in sub-freezing temperatures.
2. Engine starting: AGM handles high-current bursts for cranking applications.
3. Seasonal or infrequent use: Systems under 300 total lifetime cycles may never reach AGM's cycle limit.
4. Vibration tolerance: AGM's sealed, compressed glass mat construction resists vibration damage in mobile installations -- boats, trailers, and vehicles on unpaved roads.

Note that "maintenance-free" means no water additions. AGM batteries still require proper charge profiles, temperature monitoring, and voltage regulation. Incorrect charging destroys AGM cells faster than FLA.

The WindyNation 400W kit with 300Ah AGM (WindyNation 400W Mono Kit with 1500W VertaMax Inverter + 300Ah AGM) increases storage to 1,800Wh nameplate (900Wh usable at 50% DoD) for an advertised price of $1,637. That works out to $0.91/Wh on nameplate -- still more than double the Eco-Worthy LiFePO4's $0.45/Wh. On a usable-capacity basis, the gap widens further because AGM's 50% DoD cuts real storage in half.

For systems under 300 total lifetime cycles in cold environments, AGM remains a defensible choice. For every other use case, the numbers point to LiFePO4.

LiFePO4: Why 99% of Solar Kits Use It

311 of 314 battery-equipped kits in the OGE database use LiFePO4. That is 99.04% market share across 16 brands. This is not editorial preference. It reflects manufacturer decisions driven by cycle life, efficiency, and total ownership cost.

LiFePO4 Specs

• DoD: 80-100%
• Cycle life: 2,500-6,000 cycles at 80% DoD (EG4 LL 48V rated 7,000 cycles)
• Round-trip efficiency: 95-99% (Fire Mountain Solar)
• Self-discharge: 1-3% per month
• Weight: 25-30 lbs per 100Ah (vs 60-70 lbs for AGM)
• Cost per cycle: $1.35 (Greentech Renewables)

That 95-99% round-trip efficiency means nearly every watt from the solar array reaches the load. AGM loses 15-20% as heat. Over 2,500 daily cycles, that efficiency gap represents thousands of watt-hours recovered.

BMS: The Built-In Safety Layer

Every LiFePO4 battery includes a Battery Management System (BMS). The BMS prevents overdischarge below minimum cell voltage, overcharge above maximum cell voltage, cell-to-cell imbalance, short circuit current, and operation outside temperature limits. This is not optional -- it is integral to the chemistry.

Thermal Stability

LiFePO4's iron phosphate cathode decomposes at approximately 270°C, versus 210°C for NMC (nickel-manganese-cobalt) lithium-ion. That 60°C margin eliminates thermal runaway risk under normal operating conditions -- a critical distinction for unattended off-grid installations.

Price Trend

Market average LiFePO4 pricing has dropped from $400/kWh in 2020 to approximately $240/kWh in 2026. The EG4 48V 5.12kWh battery sells for $650-$750, representing $127-$146/kWh. Most LiFePO4 manufacturers now offer 5-10 year warranties reflecting rated cycle life, compared to 1-2 year warranties typical of AGM.

Kit Examples

• EcoFlow RIVER 2 Max: LiFePO4, 12V, 512Wh, advertised price $269 = $0.53/Wh
• Anker SOLIX C1000 Gen2: LiFePO4, 48V, 1,024Wh, advertised price $650 = $0.63/Wh
• ECO-WORTHY 200W 12V Complete Kit: LiFePO4, 12V, 1,280Wh, advertised price $540 = $0.45/Wh

The One Real Limitation

LiFePO4 only charges between 32°F and 122°F (LiTime). The BMS locks out charging below 32°F to prevent lithium plating, which causes permanent capacity loss at the cell level (REDARC Electronics). Discharge works down to -4°F.

Two mitigations exist: heated battery enclosures ($50-$100) and self-heating LiFePO4 models with internal heating elements that activate automatically before charging begins. Self-heating models carry a $50-$80 premium over standard LiFePO4 at the same capacity.

Weight Advantage

A 100Ah LiFePO4 battery weighs 25-30 lbs. A 100Ah AGM weighs 60-70 lbs. That is a 40-60% weight reduction for mobile applications -- RVs, vans, boats, and portable setups. For a 400Ah bank, the difference is 120-160 lbs of dead weight eliminated.

The EcoFlow RIVER 3 (EcoFlow RIVER 3) at 245Wh and $199 demonstrates the extreme portability end of LiFePO4: a complete power station under 8 lbs with integrated inverter, BMS, and MPPT controller.

Cold-weather charging is the only real limitation. It has solutions.

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Lifetime Cost Per Cycle: The Number That Ends the Debate

$4.20 per usable cycle per kWh for AGM versus $0.22 for LiFePO4. Upfront price is the wrong metric. Cost per usable cycle is the number that determines which battery actually costs less.

The Math

WindyNation AGM kit (WindyNation 400W Complete Off-Grid Kit):

• Real build cost: $1,259
• Nameplate capacity: 1,200Wh
• Usable at 50% DoD: 600Wh (0.6 kWh)
• Cycle life: 500 cycles
• Cost per usable cycle per kWh: $1,259 / (500 x 0.6) = $4.20/cycle-kWh

Eco-Worthy LiFePO4 kit (ECO-WORTHY 200W 12V Complete Kit):

• Real build cost: $575
• Nameplate capacity: 1,280Wh
• Usable at 80% DoD: 1,024Wh (1.024 kWh)
• Cycle life: 2,500 cycles
• Cost per usable cycle per kWh: $575 / (2,500 x 1.024) = $0.22/cycle-kWh

AGM costs 19x more per usable cycle per kWh.

The Efficiency Tax

AGM's 80-85% round-trip efficiency means 15-20% of solar harvest converts to heat before reaching the load. LiFePO4's 95-99% efficiency recovers nearly everything. Over thousands of cycles, the efficiency gap compounds into hundreds of dollars of lost solar production.

Replacement Timeline

At daily cycling:

• AGM at 500 cycles = 1.4 years before replacement
• LiFePO4 at 2,500 cycles = 6.8 years before replacement

10-Year Projection

• AGM: 7 replacements x $1,259 = $8,813
• LiFePO4: 1.5 replacements x $575 = $862

Greentech Renewables confirms the pattern in their 48V system analysis: FLA $4.59/cycle, AGM $5.27/cycle, LiFePO4 $1.35/cycle.

The Peukert Effect Penalty

Lead-acid batteries (both FLA and AGM) suffer from the Peukert Effect: a 100Ah lead-acid battery delivers approximately 100Ah over 20 hours but only 50-60Ah when drawn in 1 hour. High-draw appliances (microwaves, power tools, air conditioners) trigger this penalty. LiFePO4 maintains rated capacity regardless of discharge rate.

Why This Matters for System Design

The cost-per-cycle gap means system sizing should start with lifetime budget, not upfront budget. A buyer with $1,200 to spend today can choose a WindyNation AGM system that costs $8,813 over 10 years, or an Eco-Worthy LiFePO4 system that costs $862 over the same period. The LiFePO4 system costs less upfront and less long-term.

This is not a marginal difference. It is a 10x cost reduction over a decade of daily use.

LiFePO4 is the lowest-cost battery chemistry to own. AGM is the lowest-cost to buy.

Voltage, Wiring, and Charge Controllers by Battery Type

248 of 314 battery-equipped kits in the OGE database run at 48V. Another 45 run at 24V. Only 21 use 12V. The distribution reflects a simple electrical principle: higher voltage means lower current, which means thinner wire and less resistive loss.

Wire Cost by Voltage

For a 10-foot, 3,000W run (Off Grid Authority):

• 12V: requires 4/0 AWG copper, $80-$120
• 24V: requires 2 AWG copper, $30-$50
• 48V: requires 6 AWG copper, $12-$20

The sizing rule used by professional installers: under 1kW, use 12V. Between 1-3kW, use 24V. Above 3kW, use 48V.

Charge Controller Requirements by Chemistry

LiFePO4: Requires MPPT charge controller with a LiFePO4 charging profile. Key settings: bulk/absorb voltage 14.4V (for 12V systems), float voltage 13.5V. Temperature compensation must be disabled. Equalization mode must be disabled. Both settings, standard on lead-acid profiles, will damage LiFePO4 cells.

AGM: Standard AGM preset on most MPPT and PWM controllers. Bulk/absorb voltage 14.7V, float voltage 13.8V. Temperature compensation ON -- AGM charge voltage must decrease as temperature rises.

FLA: Requires equalization mode enabled, running every 30-90 days to balance cells. Standard lead-acid profile otherwise.

PWM vs MPPT for LiFePO4

PWM controllers work with lead-acid because they tolerate the 14.7V absorption voltage and gradual taper. LiFePO4's flat discharge curve and precise voltage requirements make MPPT the correct choice. PWM controllers can overcharge LiFePO4 cells past their 14.6V safety threshold.

All-in-One Stations

Portable power stations from EcoFlow, Bluetti, and Anker handle charge control internally. The EcoFlow RIVER 3 and similar units include integrated MPPT controllers, inverters, and BMS in a single enclosure. No external charge controller selection required.

Voltage and Chemistry Interaction

Higher voltage systems pair naturally with LiFePO4. The 248 kits running at 48V in the OGE database all use LiFePO4. AGM batteries at 48V require four 12V batteries in series, compounding the maintenance burden and increasing the risk of cell imbalance. LiFePO4's built-in BMS handles cell balancing automatically, making multi-battery series strings manageable without external monitoring.

For 12V systems, both AGM and LiFePO4 work as single-battery configurations. The 21 kits at 12V in the database include both the WindyNation AGM kits and smaller LiFePO4 portables like the EcoFlow RIVER 2 Max.

Voltage first. Chemistry second. Controller third.

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Which Battery Type for Your Use Case

The specs are clear. Match chemistry to situation.

Scenario 1: Weekend RV or Van Life

LiFePO4 12V, 500-1,500Wh. Weight matters in mobile applications -- LiFePO4 saves 30-40 lbs per 100Ah over AGM. The EcoFlow RIVER 2 Max (512Wh, $269) covers light weekend use: phone charging, LED lighting, small fans. The ECO-WORTHY 200W 12V Complete Kit (1,280Wh, $540) handles full weekend loads including a 12V fridge and laptop charging.

Scenario 2: Full-Time Off-Grid Cabin

LiFePO4 48V, 5,000-10,000Wh. Daily cycling demands maximum cycle life and efficiency. 248 kits in the OGE database run at 48V with LiFePO4. At 2,500-6,000 cycles, a properly sized LiFePO4 bank lasts 7-16 years of daily use. A full-time cabin drawing 3,000Wh/day needs a minimum 3,750Wh bank at 80% DoD -- or 6,000Wh at 50% DoD with AGM. The AGM path requires double the battery capacity and 2-3x the weight for the same usable energy. Over 10 years, the cost-per-cycle analysis from the previous section applies directly: $862 (LiFePO4) vs $8,813 (AGM).

Scenario 3: Emergency Backup

LiFePO4 any voltage, 1,000-3,000Wh. Low self-discharge (1-3%/month) keeps the battery ready for months without maintenance. The Anker SOLIX C1000 Gen2 (1,024Wh, $650) delivers enough capacity for 24-48 hours of critical loads.

Scenario 4: Cold Climate Cabin (Below 32F Regularly)

AGM 12V is the simple option. The WindyNation 400W Complete Off-Grid Kit ($1,149 AGM) charges in sub-freezing conditions without restriction. The alternative: LiFePO4 with a heated enclosure ($50-$100) or a self-heating LiFePO4 model at a $50-$80 premium per battery. The heated LiFePO4 path costs more upfront but saves on replacement cycles -- the same 19x cost-per-cycle advantage applies once charging is solved.

Scenario 5: Starter System Under $300

A single Renogy AGM 100Ah ($189.99) plus a PWM charge controller fits tight initial budgets. Plan to upgrade to LiFePO4 within 2 years as the AGM approaches its cycle limit.

Decision Table

Buying the lowest-priced battery regardless of use case is the most common and most costly mistake. LiFePO4 is the default for daily cycling. AGM wins only in cold-charging scenarios and ultra-low initial budgets. The cost-per-cycle math from the previous section holds across every scenario in this table.

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Frequently Asked Questions

What is the difference between a deep cycle and a regular battery?

A deep cycle battery uses thicker plates designed for repeated partial discharge and recharge. A regular (starting) battery uses thin plates optimized for brief, high-current bursts. Using a starting battery for solar cycling destroys it within 50-100 cycles. Deep cycle batteries last 300-6,000+ cycles depending on chemistry and DoD.

Is LiFePO4 the same as lithium-ion?

No. LiFePO4 (lithium iron phosphate) is a subset of lithium-ion chemistry. Standard Li-ion (NMC/NCA) uses nickel-manganese-cobalt or nickel-cobalt-aluminum cathodes. LiFePO4 trades energy density for thermal stability -- it does not experience thermal runaway. Only 1 of 314 battery kits in the OGE database uses non-LiFePO4 Li-ion.

How long does a deep cycle battery last?

At daily cycling: AGM at 50% DoD lasts approximately 1.4 years (500 cycles). LiFePO4 at 80% DoD lasts approximately 6.8 years (2,500 cycles). Premium LiFePO4 like the EG4 LL rated at 7,000 cycles can last 19+ years of daily use.

Can I use a deep cycle marine battery for solar?

A true deep cycle marine battery works for solar, but a marine "starting/deep cycle" dual-purpose battery does not perform well under daily cycling. Check the manufacturer spec sheet for DoD rating and cycle count. If neither is listed, assume it is a starting battery with a deep cycle label.

What does depth of discharge (DoD) mean?

DoD is the percentage of total battery capacity used before recharging. A 100Ah battery discharged to 50Ah remaining is at 50% DoD. AGM batteries should not exceed 50% DoD. LiFePO4 batteries operate safely at 80-100% DoD. Lower DoD extends cycle life exponentially.

Can LiFePO4 batteries charge in cold weather?

LiFePO4 batteries discharge down to -4°F but only charge between 32°F and 122°F (LiTime). Charging below 32°F causes lithium plating -- permanent, irreversible capacity loss at the cell level (REDARC Electronics). The BMS locks out charging below freezing. Solutions: heated battery enclosures ($50-$100) or self-heating LiFePO4 models.

Do I need a special charge controller for LiFePO4?

Yes. LiFePO4 requires an MPPT charge controller with a LiFePO4 charging profile. Critical settings: bulk/absorb at 14.4V, float at 13.5V, temperature compensation disabled, equalization disabled. Using an AGM or FLA profile risks overcharging past 14.6V, which triggers BMS shutdown or causes cell damage.

What is the lowest-cost deep cycle battery per cycle?

LiFePO4 at $1.35/cycle (Greentech Renewables). FLA costs $4.59/cycle. AGM costs $5.27/cycle. Per usable cycle per kWh, the gap widens further: LiFePO4 delivers 80-100% of nameplate capacity per cycle versus 50% for AGM. Factor in the Peukert Effect penalty on lead-acid under high loads, and the real-world gap is even larger. LiFePO4 has the lowest cost per cycle by every metric.

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Kit prices checked Apr 5, 2026. Prices fluctuate — verify before purchase.