Battery Types Explained

When I first priced batteries for my backup power system, the sticker shock pushed me straight to cheap lead‑acid. I figured “a battery is a battery,” right? Six months later, after watching them struggle to power even basic loads and constantly needing water, I replaced them with LiFePO₄. Lesson learned the expensive way.

Here’s the real-world breakdown I wish someone had given me before I spent twice on batteries. No marketing fluff—just what actually matters when your power goes out.

What Actually Matters (Not What Salespeople Tell You)

After three different battery setups and more than a few midnight power outages, here’s what I’ve learned really counts:

• Usable capacity (DoD): How much you can actually use without destroying the battery. Marketing says 100Ah, reality might be 50Ah.
• Cycle life: How many full charge/discharge cycles before you’re shopping again
• Charge speed: Whether you can recharge during a short sunny window or need all day
• Temperature performance: Because batteries in garages get hot, and cold kills capacity
• Safety and maintenance: Whether you’re checking water levels monthly or just forgetting they exist

Battery Types in 2025 (Real-World Performance)

Flooded Lead‑Acid (FLA) - “The Learning Battery”

My experience: Started here because $200 for 100Ah seemed like a steal. Reality check: you can only use about 50Ah without damaging them, and they need distilled water every month. I had four golf cart batteries that worked fine until it got cold—then they delivered maybe 60% capacity. The constant maintenance and poor cold weather performance made me upgrade after one winter.

Real specs:

• Usable capacity: 50% (50Ah from 100Ah battery)
• Cycle life: 300-500 cycles to 50% capacity
• Charge time: 8-12 hours for full charge
• Maintenance: Monthly water checks, terminal cleaning
• Temperature range: -4°F to 122°F (-20°C to 50°C), 30-50% capacity loss below freezing
• Cost per usable kWh: $400-600 over lifetime
• Safety: Low risk, but hydrogen gas production requires ventilation

Bottom line: Great for learning, terrible for reliability. If budget is everything, they work, but factor in replacement costs.

AGM (Absorbed Glass Mat) - “The Compromise”

My experience: Upgraded to AGM thinking I’d solved the maintenance issue. They do charge faster than flooded and don’t need water, but you’re still stuck at ~50% usable capacity. I had a set of Lifeline AGMs that lasted about 4 years with careful use. Better than flooded for sure, but still heavy and limited.

Real specs:

• Usable capacity: 50-60% (50-60Ah from 100Ah battery)
• Cycle life: 400-600 cycles to 50% capacity
• Charge time: 6-10 hours for full charge
• Maintenance: None required, sealed design
• Temperature range: 5°F to 122°F (-15°C to 50°C), 20-40% capacity loss below freezing
• Cost per usable kWh: $350-550 over lifetime
• Safety: Low risk, sealed design prevents acid spills

Bottom line: Good middle ground if you need lead-acid reliability without maintenance, but the limited usable capacity gets frustrating fast.

Gel - “The Finicky Option”

My experience: Tried these once because a dealer swore by them. Big mistake. They’re incredibly sensitive to charging voltage - just 0.2V too high and you can damage them permanently. I learned this the hard way when my charge controller hiccupped. They work fine in perfect conditions but are unforgiving in real-world setups.

Real specs:

• Usable capacity: 50-60% (50-60Ah from 100Ah battery)
• Cycle life: 500-700 cycles to 50% capacity
• Charge time: 8-12 hours for full charge
• Maintenance: None required, sealed design
• Temperature range: 14°F to 140°F (-10°C to 60°C), 15-30% capacity loss below freezing
• Cost per usable kWh: $400-600 over lifetime
• Safety: Low risk, but overcharging can cause permanent damage

Bottom line: Skip unless you have very specific needs and perfect charging control. Not worth the headache for most home systems.

Standard Lithium-ion (NMC) - “The Consumer Choice”

My experience: These are what you’ll find in most affordable solar generators and power stations. They’re lighter than lead-acid and don’t need maintenance, but they don’t last as long as LiFePO₄. I had an NMC battery in a portable generator that started losing capacity after 2 years of regular use.

Real specs:

• Usable capacity: 80-90% (80-90Ah from 100Ah battery)
• Cycle life: 800-1,200 cycles to 80% capacity
• Charge time: 2-4 hours for full charge
• Maintenance: None required, built-in BMS
• Temperature range: 32°F to 113°F (0°C to 45°C), 10-20% capacity loss below freezing
• Cost per usable kWh: $300-450 over lifetime
• Safety: Medium risk, requires proper BMS to prevent thermal runaway

Bottom line: Good for consumer electronics and occasional use. Not ideal for daily cycling or long-term storage needs.

Lithium Iron Phosphate (LiFePO₄) - “The Game Changer”

My experience: After cycling through lead-acid options, I invested in a 400Ah LiFePO₄ bank ($2,400). Game changer. I can use 380Ah of actual capacity (vs 200Ah from equivalent lead-acid), they charge in 2-3 hours instead of 8+, and they’ve been rock solid for 3 years with zero maintenance. The upfront cost hurt, but I’m not replacing them every few years like lead-acid batteries.

Real specs:

• Usable capacity: 90-95% (90-95Ah from 100Ah battery)
• Cycle life: 3,000-6,000 cycles to 80% capacity
• Charge time: 2-4 hours for full charge
• Maintenance: None required, built-in BMS
• Temperature range: -4°F to 140°F (-20°C to 60°C), minimal capacity loss in cold
• Cost per usable kWh: $200-350 over lifetime
• Safety: Low risk, stable chemistry, built-in BMS prevents issues

Bottom line: Higher upfront cost, but the usable capacity, longevity, and charging speed make them worth it for serious backup power. Built-in BMS handles the safety stuff automatically.

Sodium-ion - “The Emerging Contender”

My experience: Just starting to see these in affordable solar generators. They’re cheaper than lithium but have some quirks. I tested a small sodium-ion battery bank—it worked well but took longer to charge than expected and had slightly less capacity in cold weather.

Real specs:

• Usable capacity: 85-90% (85-90Ah from 100Ah battery)
• Cycle life: 2,000-4,000 cycles to 80% capacity
• Charge time: 3-6 hours for full charge
• Maintenance: None required, built-in BMS
• Temperature range: 14°F to 113°F (-10°C to 45°C), 15-25% capacity loss below freezing
• Cost per usable kWh: $150-250 over lifetime
• Safety: Medium risk, newer technology with evolving BMS requirements

Bottom line: Promising cheaper alternative to lithium with good performance. Watch for real-world longevity data as the technology matures.

Battery Cost Comparison (2025 Pricing)

Based on real market data for 100Ah equivalent systems:

Costs based on 100Ah equivalent capacity, 500 cycles/year usage. LiFePO₄ shows best long-term value despite higher upfront cost.

Charging Requirements & Compatibility

Lead-Acid (Flooded/AGM/Gel):

• Charge voltage: 13.8-14.4V (absorption), 13.2-13.8V (float)
• Charge current: 10-30% of capacity (10-30A for 100Ah battery)
• Controller type: PWM or MPPT, voltage regulation critical
• Sensitivity: Moderate - can handle some overcharge but not chronic

Lithium-ion (NMC/LiFePO₄):

• Charge voltage: 14.2-14.6V (NMC), 14.4-14.6V (LiFePO₄)
• Charge current: 20-100% of capacity (20-100A for 100Ah battery)
• Controller type: MPPT required, current limiting essential
• Sensitivity: High - BMS critical, overcharge can cause thermal runaway

Sodium-ion:

• Charge voltage: 13.6-14.0V
• Charge current: 15-50% of capacity
• Controller type: MPPT recommended
• Sensitivity: Medium - evolving BMS standards

Safety & Maintenance Comparison

Lead-Acid Batteries:

• Thermal runaway risk: Low - stable chemistry
• Gas production: High - hydrogen/oxygen from charging, requires ventilation
• Acid spills: High risk with flooded batteries
• BMS required: No
• Maintenance schedule: Monthly water checks, quarterly cleaning
• Storage: Keep charged, cool temperatures

Lithium Batteries (NMC/LiFePO₄):

• Thermal runaway risk: Medium-High (NMC), Low (LiFePO₄)
• Gas production: None during normal operation
• Acid spills: None
• BMS required: Yes - critical for safety
• Maintenance schedule: None required
• Storage: Can be stored discharged, wide temperature range

Sodium-ion:

• Thermal runaway risk: Medium - still being studied
• Gas production: Minimal
• Acid spills: None
• BMS required: Yes - evolving requirements
• Maintenance schedule: None required
• Storage: Similar to lithium, but monitor for self-discharge

Key Takeaways for Your Battery Decision

Don’t get caught up in amp-hour marketing. A 100Ah lead-acid gives you maybe 50Ah usable. A 100Ah LiFePO₄ gives you 95Ah usable. Do the math on actual capacity, not nameplate ratings.

For most home backup systems in 2025: LiFePO₄ is the clear winner despite higher upfront cost. The usable capacity (95% vs 50%), cycle life (6000+ vs 500), and safety advantages make them cost-effective over 5+ years.

Recommended Gear

• Quality LiFePO₄ packs with low‑temp charging protection
• MPPT charge controller matched to array voltage/current
• Proper fusing, shutoffs, and bus bars; shunt‑based battery monitor

FAQs

Sources

• Manufacturer specs (DoD/cycle life), reputable solar forum test data
• Real-world testing data from off-grid installations
• Battery University research and testing protocols

Related Guides

• Solar Generators Complete Buying Guide: How battery chemistry affects solar generator performance and why LiFePO₄ units outperform lithium-ion
• Home Backup Power Systems Complete Guide: Complete system design including battery bank sizing and integration
• DIY Home Battery Backup System: Step-by-step battery installation with component selection
• Generator Safety Guide: Safe charging practices and backup power system maintenance