16650 Batteries: How to Choose, Use, and Compare

16650 batteries are cylindrical lithium‑ion cells measuring 16 mm in diameter and about 65 mm in length. They offer a nominal 3.6–3.7 V and typically 2000–2500 mAh capacity. Think of them as a slimmer alternative to 18650 cells for devices designed around a narrower tube or tighter battery compartments.

Key Specs at a Glance

• Size: 16 mm diameter × ~65 mm length (protected cells can be ~68–70 mm)
• Voltage: 3.6–3.7 V nominal; 4.2 V full charge
• Capacity: ~2000–2500 mAh (7.2–9.3 Wh)
• Weight: ~35–45 g
• Common chemistries: INR/IMR/ICR (check continuous discharge rating)
• Top style: button‑top or flat‑top (match your device’s contact design)
• Protection: protected (safer, longer) vs unprotected (shorter, higher current potential)

When to Choose — and When to Avoid

• Choose 16650 if your device specifically supports 16650, or if it accepts both 16650 and 18650 with a sleeve/adapter.
• Choose 16650 when you need a slimmer cell than 18650 to reduce handle diameter or fit a narrow tube.
• Avoid 16650 if your device requires 18650 only (tight battery tube) or if it expects two CR123A cells (higher voltage).
• Avoid 16650 when maximum runtime is critical and size allows 18650 or larger; an 18650 usually offers 3000–3600 mAh.

Buying Checklist

• Compatibility: confirm your device lists 16650 support; check required top style and maximum cell length.
• Protected vs unprotected: use protected cells for general consumer devices; unprotected only if the device has its own protection and needs higher current or shorter length.
• Current rating: match the cell’s continuous discharge rating (CDR) to your device. Example: for a 6–8 W light (≈2 A), a 10 A CDR cell is ample.
• Capacity vs performance: higher mAh usually means longer runtime but may trade peak current. Choose based on your load.
• Reputable suppliers: stick to known brands and sellers to reduce risk of rewrapped or overstated cells.

Charging and Care

• Use a quality Li‑ion charger set for 4.2 V termination. Avoid “universal” chargers without Li‑ion modes.
• Charge rate: 0.5 C is a safe rule of thumb (e.g., ~1.0–1.2 A for a 2000–2400 mAh cell).
• Do not over‑discharge: recharge before the cell drops below ~2.8–3.0 V.
• Storage: keep at ~40–60% state of charge in a cool, dry place (50–77 °F / 10–25 °C).
• Cycle life: typically ~300–500 cycles; gentle charging, moderate temperatures, and avoiding full/deep cycles can extend to ~500–800.
• Safety: never carry loose cells; use a case. Do not mix old and new cells in multi‑cell devices.

Runtime Examples (Estimates)

• Low‑drain sensor at 100 mA: ~18–22 hours on a 2200 mAh cell.
• Flashlight drawing 1 A: ~2 hours (allowing for voltage sag and driver losses).
• High mode drawing 3 A: ~40–50 minutes sustained (thermal/driver limits may reduce this).

Actual runtime depends on device efficiency, regulation, cut‑off voltage, and temperature.

Alternatives and Comparisons

Cell	Size	Nominal V	Typical Capacity	Notes
16340 (RCR123A)	16×34 mm	3.6–3.7 V	600–900 mAh	Much shorter; not interchangeable with 16650 length.
16650	16×65 mm	3.6–3.7 V	2000–2500 mAh	Slimmer alternative to 18650 when supported.
18650	18×65 mm	3.6–3.7 V	3000–3600 mAh	Best for longer runtime if diameter allows.
CR123A (primary)	16×34 mm	3.0 V	~1400–1700 mAh	Non‑rechargeable; different voltage and length.

Compatibility Notes

• 16650 is not a drop‑in replacement for a single CR123A: it is longer and a different voltage.
• Some flashlights accept 18650 or 16650 with a spacer/sleeve; check your manual for approved cell types.
• Protected 16650 cells can be a few millimeters longer; ensure your device springs and tube tolerate the added length.

FAQ

Can I use a 16650 in a device made for 18650?

Only if the device manual says it supports 16650 (often with a sleeve). Without support, the smaller diameter can cause poor contact or rattle.

Is 16650 the same as CR123A?

No. 16650 is much longer and rechargeable at 3.6–3.7 V nominal. CR123A is shorter (16×34 mm) and typically 3.0 V non‑rechargeable.

Should I buy protected or unprotected?

Choose protected for most consumer devices for added over‑current, over‑charge, and over‑discharge protection. Use unprotected only if your device has built‑in protection and needs shorter length or higher current.

Button‑top or flat‑top?

Button‑tops help reach recessed contacts and are common in flashlights. Flat‑tops may be required for battery packs or tight compartments. Check your device’s contact design.

What charger do I need?

Use a lithium‑ion charger with 4.2 V termination and a charge current around 0.5 C (~1.0–1.2 A for 2000–2400 mAh). Avoid trickle charging; remove the cell when full.