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LIPO Safety and Charging Guidelines

RC Flight Safety Lithium-Polymer Batteries

LiPo Battery Safety & Charging Guide

LiPo batteries deliver high power at low weight—perfect for RC flying. They also demand careful handling. This guide summarizes the practices we require and recommend at the field and in your shop.

Overview

LiPo (Lithium-ion polymer) packs are safe when treated correctly. Most incidents are caused by over-charging, physical damage, short circuits, or improper storage. Mitigate risks by following the steps below and using proper charging gear.

Never charge unattended. If you must step away, stop the charge and disconnect.

The Golden Rules

  • Balance-charge every time (use the main leads and the balance lead).
  • Verify correct chemistry (LiPo) and cell count (S-count) on the charger.
  • Default to 1C charge rate unless the pack says it supports higher.
  • Use a LiPo-safe bag or fire-resistant container while charging.
  • Keep a bucket of dry sand within reach; know where the extinguisher is.
  • Inspect packs before and after each flight (puffing, damage, heat).
  • Stop using any pack that is puffed, leaking, hot, or crashed.
  • Store at ~3.80V per cell (storage mode), cool & dry, in a metal box.
  • Do not exceed pack C-rating or ESC/current limits.
  • Label your packs with name, capacity, S-count, and purchase date.

Charging: Step-by-Step

  1. Place the pack in a LiPo-safe bag on a non-flammable surface (concrete, tile, or metal tray).
  2. Set charger to Balance Charge → LiPo → correct S-count (e.g., 3S/4S).
  3. Set current (amps) to pack capacity × C-rate (see calculator below).
  4. Connect main leads and balance lead; check polarity and tight connections.
  5. Start the charge and monitor. Pack should stay cool to mildly warm.
  6. Completion voltage is about 4.20V per cell (e.g., 12.6V for 3S).
  7. Let the pack rest a few minutes before installation or storage.
Pro tip: If a pack returns from flight unusually hot, let it cool to room temp before charging. Heat + charging accelerates degradation.

Charge Rates & Quick Calculator

1C = pack capacity (Ah). For a 2200 mAh (2.2 Ah) pack, 1C = 2.2 A. Some packs support 2C+ charging—only use that if the label/manual explicitly allows it.

Typical Settings

Pack 1C Current Full Voltage
2S 2200 mAh 2.2 A 8.40 V
3S 2200 mAh 2.2 A 12.60 V
4S 1500 mAh 1.5 A 16.80 V
6S 5000 mAh 5.0 A 25.20 V

Calculator

Note: If your charger reads cell voltages significantly imbalanced (>0.05–0.10V spread), stop and balance-charge at a lower current, or retire the pack.

Storage & Transport

Storage Targets

State Per-Cell Voltage Notes
Storage 3.75–3.85 V Use charger’s Storage mode.
Min (avoid) ≤ 3.3 V Risk of damage; don’t fly below this under load.
Max (full) 4.20 V Do not exceed. Never 4.25+ V.

Transport

  • Use LiPo-safe bags or a vented metal container (no airtight lids).
  • Keep packs separated to prevent lead contact/shorts.
  • Avoid leaving packs in a hot car. Heat accelerates puffing and risk.
  • Bring sand/metal tray for field charging; keep area clear of combustibles.

Inspection & When to Retire a Pack

Before Each Use

  • No swelling/puffing beyond slight “softness”.
  • No cuts, dents, or punctures in the pouch or heat-shrink.
  • Leads and balance plug secure; no exposed copper.
  • Cells within ~0.02–0.05 V of each other at rest.

Retire If You See

  • Visible swelling, hissing, or chemical odor.
  • Pack gets hot at low loads or during gentle charge.
  • Severe imbalance that won’t correct with balance charge.
  • After a crash with suspected physical damage.

Field Charging Setup

Do

  • Charge on concrete/asphalt or a metal baking tray.
  • Use a LiPo bag and a quality balance charger.
  • Keep sand and an ABC extinguisher nearby.
  • Stay within arm’s reach while charging.

Don’t

  • Charge on grass, wood benches, or car interiors.
  • Leave on full charge for days—store at 3.8V/cell.
  • Use damaged, puffy, or hot packs.
  • Daisy-chain sketchy adapters; keep wiring tidy.

Power Sources

  • Use regulated AC/DC supplies or a healthy deep-cycle battery.
  • Fuse DC leads; avoid alligator-clip chaos.
  • Keep chargers shaded/cool for accurate sensing.

Fire / Emergency Response

  1. If a pack smokes or vents: Unplug if safe. Move people back.
  2. Use dry sand to smother flames and contain the pack. An ABC extinguisher helps with surrounding materials.
  3. If it’s only heating without flame, place the pack outdoors on concrete/metal and monitor—packs often flare more than once.
  4. After it cools completely, treat as hazardous and take to a battery recycler.
Note: Li-ion polymer (not lithium-metal) fires can be cooled with water, but only if it’s safe for your surroundings and electronics. Our field standard is dry sand first, water only to prevent spread if needed.

Disposal & Recycling

  • Discharge the pack fully with a resistor/discharger or your charger’s “Discharge” function (low current, supervised). Do not puncture the pack.
  • Tape over exposed terminals.
  • Bring to a battery recycling center (home improvement stores often accept rechargeables). Avoid the outdated “saltwater soak” method.

FAQ

What voltage is “empty” for a LiPo?

Under load, try to land before cells sag below ~3.5V. At rest after the flight, you’ll usually read ~3.7–3.8V/cell. Consistently going to ≤3.3V/cell damages packs.

Can I parallel-charge?

Yes, but only packs of the same cell count and similar state of charge (within ~0.1V/cell). Use a quality board with fuses; total current = sum of individual 1C rates.

My pack is slightly puffy—safe?

Minor soft puffing is a warning—reduce loads and monitor closely. Visible ballooning, heat, or odor: retire immediately.

Do I need to “break in” new packs?

Not strictly, but the first few cycles at modest discharge and 1C charges can improve longevity.

Printable Checklists

Pre-Charge Checklist

  • Pack passes visual inspection (no damage/puffing).
  • Correct chemistry & S-count set on charger.
  • LiPo bag used on non-flammable surface.
  • Charge current set to ≤ rated C.
  • Sand/extinguisher ready; stay in line of sight.

Post-Flight / Storage

  • Let pack cool to room temperature.
  • Storage charge to ~3.8V/cell if not flying within 24h.
  • Log pack usage/IR if you track health.
  • Store in metal box (vented), cool & dry place.

This page is for hobby guidance at our field. Always follow your charger’s manual and pack manufacturer instructions.