Battery Chemistry Guide

Battery Chemistry Guide

Choosing the right battery chemistry for your deployment is critical. The wrong choice leads to shortened battery life, safety hazards, or a node that fails in cold weather.

Li-ion 18650 Cells

The 18650 is the workhorse battery for DIY LoRa nodes. Named for its dimensions (18mm × 65mm), it is widely available, well-understood, and supported by most mid-range device designs with a holder.

Warning: Most 18650 cells sold on Amazon are counterfeit. A cell labelled 6000mAh from an unknown brand is physically impossible — the best genuine 18650 cells reach ~3500mAh. Buy from reputable electronics retailers only.

Recommended 18650 Cells

All three options are equivalent for LoRa node use. The 8–10A max current is far above the <200 mA draw of typical nodes, so any of these cells will work well. Buy protected cells — the protection circuit prevents over-discharge which can damage the cell.

21700 Cells

21700 cells are slightly larger (21mm × 70mm) and offer higher capacity. Fewer devices have 21700 holders but they can be used in custom builds or with adapter sleeves.

LiPo Packs

Lithium polymer packs in various capacities with JST connectors are the standard battery choice for devices without 18650 holders (Heltec V3, many LilyGo boards). Match the connector type carefully.

LiPo caution: LiPo cells can swell, catch fire, or vent if overcharged, over-discharged, punctured, or charged at low temperatures. Use only with a proper charge controller. Never charge below 0°C. For unattended outdoor deployments in cold climates, prefer Li-ion 18650 or LiFePO4 over LiPo.

LiFePO4 (Lithium Iron Phosphate)

LiFePO4 is strongly preferred for outdoor and cold-weather deployments. Key advantages over Li-ion/LiPo:

• Temperature tolerance: Operates and can be charged at much lower temperatures (–20°C for charging, –40°C for discharge)
• Safety: Much less prone to thermal runaway; does not catch fire when punctured or overcharged
• Cycle life: 2000–3000 cycles vs. 300–500 for standard Li-ion
• Discharge curve: Flat 3.2V nominal vs. 3.7V for Li-ion — verify your device supports 3.2V operation

Trade-off: Lower energy density than Li-ion. A LiFePO4 pack of the same physical size will have less capacity than a Li-ion pack. Plan for ~50% capacity loss at –40°F even with LiFePO4, and size accordingly.

Battery Chemistry Comparison