D Batteries

D Batteries (Size D) — How to Choose the Right Type

D batteries (IEC size D; often labeled LR20 for alkaline, HR20 for NiMH) are among the largest common cylindrical cells used in high‑drain or long‑runtime gear: camping lanterns, emergency/weather radios, motorized toys, and some tools and instruments. Their larger volume delivers longer runtime than C, AA, or AAA in the same device type.

Quick Decision Guide

• Emergency kits, long storage, infrequent use: choose alkaline D (reliable 1.5 V, 5–10 year shelf life).
• Frequent use (weekly/daily), high drain, cost control: choose rechargeable NiMH D (1.2 V nominal; low‑self‑discharge preferred).
• Ultra low‑drain, lowest upfront cost only: zinc‑carbon D (shorter life; higher leak risk). Use sparingly.
• Lithium D: many are 3.6 V industrial cells (e.g., lithium‑thionyl chloride). Use only if your device explicitly specifies them. They are not drop‑in for 1.5 V D devices.

What to Know About Voltage and Fit

• Size: approx. 61.5 mm length × 33.2 mm diameter.
• Standard consumer D devices expect ~1.5 V per cell (alkaline/zinc‑carbon). NiMH rechargeables are ~1.2 V and usually work, but some devices with strict low‑voltage cutoffs may shut off earlier.
• Rechargeable Li‑ion “D” cells are typically 3.6/3.7 V or use internal regulators to 1.5 V. Only use if the product states compatibility and provides clear capacity specs.

Common Use Cases

• Lanterns and large flashlights (camping, emergency response).
• Portable/emergency radios and sirens.
• Motorized toys and science kits needing high surge current.
• Air pumps, small appliances, and some test/industrial instruments (check voltage type).

Type Comparison

Type	Nominal Voltage	Typical Capacity	Best For	Shelf Life	Notes
Alkaline (LR20)	1.5 V	~12,000–18,000 mAh at low drain (15–25 Wh)	Emergency kits, occasional use	~5–10 years	Good leak resistance; performance drops in very high drain and cold.
NiMH Rechargeable (HR20)	1.2 V	~8,000–10,000 mAh (9–12 Wh); low‑self‑discharge types hold charge better	Frequent use, high drain	~2–3 years to 70–80% capacity (varies)	Recharge hundreds of times; needs compatible charger.
Zinc‑Carbon (R20)	1.5 V	~4,000–8,000 mAh (low drain only)	Very low‑drain, budget‑sensitive	~2–3 years	Higher leak risk; weak in high drain.
Lithium (industrial)	Often 3.6 V	High for specialized loads	Meters, sensors (device‑specified)	5–20+ years (device dependent)	Not for standard 1.5 V D devices unless specified.

Runtime Estimates (Rule‑of‑Thumb)

Runtime varies with load, temperature, and device cutoff. Use these simple estimates to plan:

• 3‑cell lantern drawing 0.5 A total: Alkaline ~10–20 hours; NiMH ~8–15 hours.
• AM/FM weather radio at low volume (~60 mA): Alkaline ~150–250 hours; NiMH ~110–170 hours.
• High‑output flashlight (~1.0 A): Alkaline ~5–10 hours; NiMH ~4–8 hours.

Tip: Devices that use multiple D cells in series increase voltage, not capacity; runtime is largely determined by the per‑cell capacity and the device’s current draw.

Buying Checklist

• Match chemistry to use: Alkaline for storage; NiMH for frequent use; avoid zinc‑carbon for high drain.
• Look for low‑self‑discharge (LSD) NiMH if you want rechargeables that hold charge for months.
• Capacity realism: Be wary of inflated mAh claims on rechargeables; reputable NiMH D cells are typically 8,000–10,000 mAh.
• Charger fit: Ensure your charger supports size D and charges cells individually at 0.5–2 A. A 10,000 mAh NiMH at 1 A needs ~12–14 hours from empty.
• Date codes and freshness: Choose recent manufacture dates for alkaline; avoid damaged or corroded packs.

Care, Storage, and Safety

• Store cool and dry (approx. 50–77°F / 10–25°C). Avoid heat, moisture, and direct sun.
• Do not mix old/new or different chemistries in the same device.
• Remove cells from devices you won’t use for 1+ months to reduce leak risk.
• Never attempt to recharge alkaline or zinc‑carbon cells.
• Recycle used batteries per local rules; many retailers accept drop‑offs.

Alternatives and Adapters

• AA‑to‑D adapters: Acceptable for low‑drain devices (clocks, basic radios). Not recommended for high drain; runtime and current capability are much lower.
• External power: For stationary gear, consider AC adapters or DC power banks if supported by the device.

FAQ

Are D and LR20 the same?

Yes. LR20 is the IEC code for alkaline D cells. HR20 is NiMH rechargeable; R20 is zinc‑carbon.

Will 1.2 V NiMH D batteries work in my 1.5 V device?

Often yes. Many devices run fine on NiMH’s slightly lower voltage, especially high‑drain products. A few devices with strict low‑voltage cutoffs may shut off earlier—test before relying on them.

Can I use lithium D cells as a direct replacement?

Only if the device specifically lists a compatible lithium D type. Many lithium D cells are 3.6 V industrial batteries and are not safe drop‑in substitutes for 1.5 V D devices.

How long do alkaline D batteries last in storage?

Typically 5–10 years when stored cool and dry. Check the package for “best by” dates and rotate stock in emergency kits.

Why do some rechargeable D cells seem weak?

Some low‑cost “D” rechargeables house smaller cells inside. Choose reputable brands listing realistic 8,000–10,000 mAh ratings and verify with user reviews or independent tests where possible.