32700 Batteries: How to Choose, Charge, and Use

32700 cells are extra-large cylindrical batteries measuring 32 mm in diameter and 70 mm in length. The format is used across chemistries—most commonly Li-ion (NMC/NCA) at ~3.6–3.7 V nominal and LiFePO4 at ~3.2 V nominal—making them popular for high-capacity packs in solar storage, 12 V systems, lighting, mobility, and backup power. This page explains how to pick the right 32700 cell and use it safely.

Specs at a Glance

Attribute	Li-ion (NMC/NCA) 32700	LiFePO4 32700
Nominal Voltage	3.6–3.7 V	3.2 V
Full Charge Voltage	4.20 V	3.65 V
Typical Capacity	5,000–7,500 mAh	5,000–6,500 mAh
Typical Continuous Discharge	10–20 A (model-dependent)	10–20 A (model-dependent)
Cycle Life (to ~80%)	~300–800 cycles	~1,500–3,000+ cycles
Strengths	Higher energy density (more Wh)	Long cycle life, thermal stability
Common Uses	High-energy packs, lighting	12 V systems, solar, backup

Values vary by brand and model; always check the datasheet for exact ratings.

When to Choose 32700

• Use if you need large capacity per cell for fewer parallel groups and longer runtime.
• Choose LiFePO4 32700 for 12 V systems (e.g., 4S ≈ 12.8 V) and long cycle life.
• Choose Li-ion 32700 when you need higher energy density (more watt-hours at similar weight/volume).
• Avoid if device space only fits 18–22 mm diameter cells; 32700 cells are 32 mm wide and may not fit standard chargers or holders.

32700 vs Other Sizes

• 32650 (32 × 65 mm): Slightly shorter; often similar chemistries but a bit less capacity. Pick 32700 for maximum runtime if space allows.
• 21700/18650: Much narrower; easier to fit in compact devices. Multiple smaller cells can match capacity but require more parallel groups.

How to Choose a 32700 Cell

1. Match Chemistry to System Voltage:
   • Li-ion: 3S ≈ 11.1 V nominal (12.6 V full), 4S ≈ 14.8 V nominal (16.8 V full).
   • LiFePO4: 4S ≈ 12.8 V nominal (14.6 V full), commonly used as a “12 V” replacement.
2. Capacity and Runtime: Higher mAh extends runtime; compare cells in the 5,000–7,500 mAh range.
3. Discharge Rating (A): Ensure the continuous current rating meets or exceeds your load; add headroom (20–30%).
4. Protection:
   • Protected cells add a small PCB for over/under‑voltage and over‑current protection; they’re longer and may not fit tight holders.
   • Unprotected cells are standard for pack building with a dedicated BMS.
5. Terminal Style: Flat‑top for packs; button‑top for some single‑cell devices. Verify your device/holder contact design.
6. Physical Fit: Diameter ~32 mm; length ~70 mm (protected cells can be longer). Confirm your charger and holder can accept 32 mm width.
7. Operating Temperature: Check datasheet for charge/discharge temperature ranges if using outdoors or under the hood.

Protected vs Unprotected

• Protected 32700: Best for stand‑alone, single‑cell use. Safer for general consumers but often longer than 70 mm; confirm fit.
• Unprotected 32700: Best for multi‑cell packs managed by a BMS. Requires proper design and assembly controls.

Charging Guidelines

• Use a chemistry‑correct charger: Li-ion charges to 4.20 V; LiFePO4 charges to 3.65 V. Do not cross‑charge.
• Method: CC/CV with typical charge rate 0.2–0.5C (e.g., 1–3 A for a 6,000 mAh cell). Lower rates increase longevity.
• Termination: Stop at ~0.05–0.1C taper current.
• Temperature: Charge at room temperature; avoid charging below 0°C or above 45°C unless permitted by the datasheet.
• Charger fit: Ensure bays accept 32 mm diameter and the cell length you use (protected cells may exceed 70 mm).

Runtime Estimate

Runtime (hours) ≈ Capacity (Ah) ÷ Load (A). Examples:

• Single 6,000 mAh cell powering a 3 A light: 6 Ah ÷ 3 A ≈ 2 hours.
• 4S2P LiFePO4 pack using eight 6,000 mAh cells (12 Ah total) at 6 A: 12 Ah ÷ 6 A ≈ 2 hours.

Real‑world runtime varies with temperature, discharge rate, cutoff voltage, and cell aging.

Pack‑Building Notes

• Use a BMS: Provides cell balancing, over/under‑voltage, and over‑current protection.
• Match cells: Same brand, model, capacity, and similar internal resistance; avoid mixing old and new cells.
• Assembly: Prefer spot‑welding nickel strips; avoid direct soldering to cells.
• Configuration: Choose S/P counts to meet voltage and capacity targets (e.g., 4S LiFePO4 for ~12.8 V nominal).
• Mechanical design: Use proper holders/insulators; secure against vibration; add fusing where appropriate.

Storage and Safety

• Store at 30–60% charge in a cool, dry place (ideally 10–25°C).
• Inspect for dents, swelling, corrosion, or torn wraps; recycle damaged cells immediately.
• Never carry loose cells with metal objects; use a case.
• Do not exceed the cell’s current or temperature ratings; follow the datasheet.
• Recycle at approved e‑waste or battery collection points; do not dispose in trash.

Common Use Cases

• Solar energy storage and portable power stations
• 12 V LiFePO4 battery replacements (4S configurations)
• E‑mobility: e‑bikes, scooters, and carts (pack form with BMS)
• High‑output LED lighting and work lights
• UPS, telecom backup, and emergency lighting

Pros and Limitations

• Pros: High capacity per cell, fewer parallel groups, robust current capability, good for energy storage.
• Limitations: Large diameter (fit issues), heavier than smaller formats, protected versions may be longer than 70 mm, chargers and holders must support 32 mm cells.

FAQ

Will a 32700 fit my flashlight or device?

Only if the battery tube and springs accommodate 32 mm diameter and the cell length. Many consumer devices are built for 18650/21700 and will not fit 32700 cells.

Do I need a special charger?

Yes. Use a charger that physically fits 32 mm cells and is set for the correct chemistry: 4.2 V termination for Li‑ion, 3.65 V for LiFePO4. Smart multi‑chemistry chargers often support both.

How long do 32700 cells last?

Li‑ion variants typically deliver ~300–800 cycles; LiFePO4 variants commonly exceed 1,500 cycles. Actual life depends on depth of discharge, temperature, and charge rate.

Should I buy protected or unprotected?

Buy protected for single‑cell, stand‑alone use where fit allows. Use unprotected cells only inside packs with a proper BMS.

Can I mix different 32700 cells in a pack?

No. Do not mix brands, capacities, chemistries, or new with aged cells. Mismatches cause imbalance, reduced performance, and safety risks.