A deep cycle battery provides sustained energy delivery through prolonged discharge cycles, designed to be regularly drained to 20-50% capacity (DoD) without damage. Unlike starter batteries, they prioritize amp-hour (Ah) capacity over short bursts of high current, using thicker plates and advanced chemistries like LiFePO4 for durability in RVs, marine, and solar systems. A 100Ah unit can deliver 5A for 20 hours before reaching 10.5V cutoff.
48V 560Ah LiFePO4 Forklift Battery
How do deep cycle batteries differ from starter batteries?
Deep cycle batteries use thicker lead plates or lithium compounds to withstand 200-3000+ deep discharges, while starter batteries deploy thin plates for brief, high-current cranking. For example, a marine starter battery might deliver 800A for 30 seconds, whereas a 100Ah deep cycle battery outputs 5A for 20 hours. Pro Tip: Never substitute starter batteries for trolling motors—shallow cycling below 50% DoD degrades them rapidly.
Structurally, deep cycle batteries—whether flooded lead-acid (FLA), AGM, or LiFePO4—prioritize plate durability. FLA batteries use antimony-lead grids with 500+ cycle lifespans at 50% DoD, while LiFePO4 leverages lithium iron phosphate cathodes for 2000+ cycles. A 12V 100Ah AGM battery weighs ~60 lbs, whereas a LiFePO4 equivalent is ~30 lbs. Transitional phases like partial-state-of-charge (PSOC) tolerance also differ: lithium handles 40-80% SoC better than lead-acid. But what if you need both cranking and cycling? Dual-purpose batteries compromise, offering 150-300 cycles at 50% DoD.
| Type | Cycle Life (80% DoD) | Weight (100Ah) |
|---|---|---|
| Flooded Lead-Acid | 500 | 60 lbs |
| AGM | 600 | 65 lbs |
| LiFePO4 | 3000 | 31 lbs |
What does amp-hour (Ah) rating mean?
Amp-hours measure a battery’s energy capacity, calculated as current (A) × discharge time (h). A 100Ah battery delivers 5A for 20h before hitting 10.5V. Real-world runtime depends on load—higher draws reduce usable Ah due to Peukert’s effect. For solar setups, 400Ah systems power 200W loads for ~10 hours (400Ah × 12V = 4.8kWh).
Ah ratings assume a 20-hour discharge rate (C/20). A 100Ah battery at C/5 (20A) might only deliver 80Ah. Lithium batteries minimize Peukert losses, maintaining ~95% rated capacity at high currents. For example, a 200Ah LiFePO4 battery running a 1000W inverter draws ~83A (1000W ÷ 12V), lasting ~2.3 hours. Lead-acid under the same load would deplete 30% faster. Pro Tip: Multiply lithium Ah by 0.8 for lead-acid equivalents. Thinking about powering a fridge? A 12V 200Ah lithium bank supports a 150W cooler for ~16 hours (200Ah × 12V × 0.8 ÷ 150W).
How does cycling affect battery lifespan?
Cycle life depends on depth of discharge (DoD)—discharging to 50% DoD yields 2-4x more cycles than 80% for lead-acid. A 12V 100Ah AGM battery rated for 600 cycles at 50% DoD drops to 300 cycles at 80% DoD. Lithium handles deeper discharges: 3000 cycles at 80% DoD vs 5000 at 50%. Temperature also matters—cycles above 30°C halve lead-acid lifespan.
Cycle counts assume full charge-discharge cycles. Partial cycles (e.g., 20% discharge twice) extend lifespan. Let’s say you discharge a 200Ah lithium battery by 40% daily. That’s equivalent to 0.4 cycles, translating to ~7,500 days (~20 years) before reaching 80% capacity. Compare that to a lead-acid battery cycled 50% daily, lasting ~500 cycles or 1.5 years. Beyond cycling, sulfation in lead-acid batteries during storage degrades plates, while lithium’s BMS prevents voltage decay. Pro Tip: Store lead-acid at full charge; lithium at 50-60% SoC for long-term health.
| Chemistry | 80% DoD Cycles | Annual Self-Discharge |
|---|---|---|
| Flooded Lead-Acid | 400 | 5%/month |
| AGM | 600 | 1-3%/month |
| LiFePO4 | 3000 | 2-3%/year |
What applications require deep cycle batteries?
Solar storage, marine trolling motors, and off-grid power rely on deep cycle batteries. Solar systems need 48V 400Ah+ LiFePO4 stacks for overnight loads, while RVs use 12V/24V 200-300Ah banks. Marine applications demand vibration-resistant AGM or lithium packs—3x lighter than flooded lead-acid. Golf carts, medical carts, and floor scrubbers use 6V or 8V batteries in series for 36-48V systems.
In solar setups, lithium’s higher DoD (90% vs 50% for lead-acid) reduces required capacity by 40%. A 10kWh lithium system equals a 20kWh lead-acid bank. For marine trolling, a 24V 60Ah lithium battery provides 1.4kWh—enough for 4 hours at 30A draw. Floor scrubbers prioritize runtime: eight 6V 220Ah lead-acid batteries (48V 220Ah) offer 10.5kWh, but lithium cuts weight by 60%. What if you’re boondocking? Lithium’s 98% efficiency vs lead-acid’s 70-85% means faster solar recharging.
Redway Battery Expert Insight
FAQs
Not recommended—starter batteries need thin plates for high-cranking amps. Deep cycle batteries prioritize sustained discharge, risking voltage sag and overheating during cranking.
How do I calculate runtime using amp-hours?
Divide Ah by device amps. A 100Ah battery running a 5A load lasts ~20h. For watts: (Ah × Voltage) ÷ Wattage = Hours (e.g., 100Ah ×12V ÷ 600W = 2 hours).
Are lithium deep cycle batteries worth the cost?
Yes for high-cycle needs: LiFePO4 lasts 5-10x longer than lead-acid, with lower self-discharge and maintenance. Break-even occurs in 2-3 years for daily users.
