By David Robinson | Updated March 24, 2022

Lithium‑ion (Li‑ion) and nickel‑metal hydride (NiMH) batteries power many of today’s portable devices. While they share the same basic purpose—storing electrical energy—they differ markedly in chemistry, performance, and safety requirements.

Lithium‑Ion Batteries

Li‑ion cells offer up to three times the energy density of NiMH cells, delivering more power for a given weight and size. They operate at higher voltages, so fewer cells are needed to reach a target voltage. However, Li‑ion chemistry is highly reactive; if a cell is overheated or over‑charged, it can ignite or explode.

Nickel‑Metal Hydride Batteries

NiMH cells provide respectable energy density but typically produce lower voltages per cell than Li‑ion. As a result, a NiMH pack must contain more cells, making it bulkier and heavier. NiMH chemistry is more stable; it does not spontaneously ignite when exposed to oxygen.

Charging Requirements

Both battery types require intelligent chargers, but the circuitry is fundamentally different. Li‑ion chargers constantly monitor voltage, current, and temperature, shutting off power when unsafe conditions are detected. Each Li‑ion chemistry may need a specific voltage and current profile; using a generic charger can cause overheating and fire.

NiMH chargers lack the sophisticated safety controls needed for Li‑ion cells. Plugging a Li‑ion battery into a NiMH charger can lead to uncontrolled charging, overheating, and even chemical fires.

For optimal safety and performance, always use a charger that is expressly designed for the battery chemistry you are charging. Consult the manufacturer’s guidelines or reputable resources such as Battery University for detailed charging procedures.