Battery Basics

Overview

Power keeps lights, comms, and navigation alive. Choose the right cells, store them properly, and estimate runtime to plan usage. Cold saps performance—keep batteries warm.

Chemistries

Different jobs, different cells.

• Alkaline: Cheap, common; poor cold performance; risk of leakage in storage.
• NiMH (rechargeable AA/AAA): Good cold performance; low‑self‑discharge types (e.g., Eneloop) store well.
• Li‑ion (18650/21700/phone packs): High energy density; good cold performance; needs proper chargers.
• LiFePO4 (LFP): Very stable and long‑cycle‑life lithium chemistry common in power stations and 12 V packs. Lower energy density than Li‑ion; heavier for the same capacity; requires a proper BMS/charger. Do not charge below ~0°C/32°F unless the pack is specifically rated/heated.

Capacity in Context

• mAh vs Wh: Convert to Wh for apples‑to‑apples. Wh ≈ (mAh × nominal voltage) ÷ 1000. AA NiMH ~1.2 V, Li‑ion ~3.6–3.7 V.
• Estimating power bank reality: A “10,000 mAh” (at 3.7 V) is ~37 Wh; expect ~30–33 Wh usable after conversion losses.

Series vs Parallel

Series adds voltage; parallel adds capacity (current/runtime). Match cell types and states; do not mix new/old cells or chemistries. Use protected packs when possible.

Cold-Weather Care

Keep cells warm close to the body; insulate devices; warm spare cells in a pocket; expect reduced capacity.

Estimating Runtime

Runtime (h) ≈ capacity (mAh) ÷ draw (mA). Duty cycle extends life: a headlamp at 200 mA with a 3,000 mAh 18650 runs ~15 h at 100% on—more at lower modes and intermittent use.

Safety Notes (Li‑ion)

• Use reputable cells and chargers; avoid damaged wraps; store spares in cases, not loose with metal.
• Don’t fully discharge Li‑ion regularly; store long‑term at ~40–60% in a cool place.

☑️ Checklist — Power Planning

• Inventory devices and cell types (AA/AAA/18650/USB‑C)
• Bring spares: at least one full extra set per critical device
• Standardize where possible (same cells across headlamps)
• Pack chargers/cables; verify current draw and connectors
• Protect from cold/wet; store lithium at ~40–60% for long term

Examples

• Winter hike: Headlamp on low (10–30 lm) for nav; warm spare 18650 in inside pocket; power bank kept warm for phone.
• Home blackout: NiMH AAs rotated; lantern on low; device charging plan by priority.

---

Common Mistakes

• Mixing new and old cells or chemistries in series devices; leaks and failures.
• Storing alkalines in devices long‑term; leakage damages gear—remove for storage.
• Pocketing bare Li‑ion cells with keys/coins; shorting/fire risk—use cases.
• Charging unattended with cheap/unvetted chargers; prefer reputable, protected chargers.
• Leaving cells in hot cars or freezing conditions for long periods; capacity loss/damage.

Key Takeaways

• Standardize cells; plan duty cycles; keep batteries warm.
• Match series/parallel properly; don’t mix old/new cells.
• Bring at least one full spare set for critical devices.

Scenario

🧭 Scenario (Winter headlamp save): 0°C and windy; light dims.
🔍 Decisions: Swap cell now; warm spare; duty cycle.
✅ Outcome: You warm a spare 18650 in a pocket, swap, and finish safely on low mode.
🧠 Lessons: Warm cells work; spares buy safety
🏋️ Drill: Standardize your devices on one cell type if possible.