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Battery and Power

Battery and Power

Answers to common questions about battery life, power management, battery chemistry, solar sizing, and long-term deployments.

How long does the battery last?

Battery life varies significantly by device type, display type, messaging activity, and whether the device is acting as a relay:

Device TypeTypical Battery LifeNotes
ESP32 client node (e.g., Heltec V3, T-Beam) 1–3 days 3000 mAh battery, moderate messaging. T-Beam with GPS active is toward the shorter end.
nRF52 client node (e.g., T114, RAK4631) 3–7 days Lower power than ESP32; no Wi-Fi radio
E-ink display device (T-Echo, Wireless Paper) 7–14 days E-ink uses power only when updating; excellent for always-on carry
Repeater node (always receiving) Hours to 1 day Always-on radio is the main draw; plan for continuous power

Power-saving tips: reduce TX power to the minimum needed for your use case; increase the sleep interval between beacon transmissions; disable GPS if not needed; use an e-ink device for always-on carry.

What battery chemistry should I use for outdoor deployments?

LiFePO4 (Lithium Iron Phosphate) is strongly preferred for any outdoor, unattended, or cold-weather deployment.

Why LiFePO4 over LiPo:

  • Temperature performance: LiFePO4 operates reliably from about –4°F (–20°C) to 140°F (60°C), while LiPo degrades significantly below 32°F (0°C) and risks damage below –4°F.
  • Safety: LiFePO4 does not undergo thermal runaway. It will not catch fire or explode if punctured, overcharged, or short-circuited. LiPo can combust under these conditions — a real concern for unattended outdoor installations.
  • Cycle life: LiFePO4 typically lasts 2,000–5,000+ charge cycles. LiPo lasts 300–500 cycles. For a permanently deployed solar-charged node, LiFePO4 can last a decade; LiPo may degrade in 1–3 years.
  • Voltage characteristics: LiFePO4 has a flatter discharge curve (steady ~3.2V per cell vs. LiPo’s declining curve), which means more consistent performance through the discharge cycle.

Important cold-weather note: Even LiFePO4 loses approximately 50% capacity at –40°F (–40°C). If deploying in Minnesota, the Dakotas, Canada, or similar climates, size your battery bank for worst-case winter temperatures — not just rated capacity.

Are cheap 18650 batteries from Amazon OK?

Be very careful. The 18650 battery market on Amazon is saturated with counterfeit and significantly overstated-capacity cells. A cell listed as “9800mAh” for $3 is physically impossible — genuine high-quality 18650 cells max out around 3,500 mAh.

Counterfeit cells often have:

  • Actual capacity 20–50% of stated capacity
  • Poor safety circuits or none at all
  • Higher internal resistance = poor performance under load
  • Increased fire/damage risk

Buy 18650 cells from reputable sources:

  • 18650batterystore.com — US-based, genuine cells, good selection
  • illumn.com — US-based specialty battery retailer
  • Brand-name cells: Samsung 30Q, Samsung 40T, Molicel P26A, Molicel P42A, Panasonic NCR18650B, LG MJ1

For outdoor deployments where capacity and reliability matter, buying genuine cells from a reputable source is worth the modest price premium over Amazon mystery cells.

How big a solar panel do I need for a repeater node?

A typical LoRa repeater node in the continental United States requires a surprisingly modest solar setup. Rules of thumb:

  • Panel: 5–10 W is adequate for most locations during summer. A 10 W panel provides comfortable margin for cloudy days.
  • Battery: Size for 3–5 days of runtime without any solar input. For a node drawing ~150 mA average: 3 days at 150 mA = 10.8 Ah minimum. A 20 Ah LiFePO4 battery provides good margin.

Regional considerations:

  • Southern US (Texas, Arizona, California): Ample sun year-round; 5–7 W panel is usually sufficient.
  • Northern US (Minnesota, North Dakota, Montana): December peak sun hours can drop to 2.5 hours/day — significantly less than the 4–6 hours/day you get in summer. A 10 W panel and a larger battery bank (30–40 Ah) is recommended for year-round operation without manual intervention.
  • Pacific Northwest: Low winter sun and frequent overcast; plan for 2–3 hours/day in winter. Size accordingly or accept that the node may need occasional charging in deep winter.

Practical formula: Daily energy consumption (Wh) ÷ peak sun hours ÷ panel efficiency (typically 80% for a real system) = panel wattage needed. Always add 50–100% margin for real-world inefficiency, dirty panels, and suboptimal panel angle.

Can I charge LiFePO4 batteries with a standard LiPo charger?

No — use only a charger designed for LiFePO4. LiFePO4 cells have a different charge voltage profile than LiPo cells (3.65V/cell max for LiFePO4 vs. 4.2V/cell for LiPo). Charging LiFePO4 with a LiPo charger will overcharge the cells, reducing their life and potentially causing damage.

Purpose-built LiFePO4 solar charge controllers and battery management systems (BMS) are widely available and not expensive. Many solar charge controllers include a LiFePO4 mode.

Should I run my node from a USB power bank?

USB power banks work well for portable and temporary deployments. They are convenient, inexpensive, and widely available.

Limitations for permanent deployment:

  • Most USB power banks shut off when they detect a low-current draw (like a standby LoRa node). This is called “low-current cutoff.” The node will stop running after a short time even if the power bank is not depleted.
  • Power banks are not designed for continuous solar charging — charging and discharging simultaneously (known as “pass-through”) degrades many power banks quickly.

For permanent outdoor deployment, use a dedicated LiFePO4 battery with a proper solar charge controller rather than a consumer power bank.

My device gets warm during operation. Is this normal?

Mild warmth is normal, particularly during active transmission or when running at high TX power. ESP32-based devices run slightly warm at 20–27 dBm TX power. This is not a concern at normal operating temperatures.

Concerns to watch for:

  • Excessive heat from the battery area may indicate a failing or improperly charged LiPo battery. Discontinue use immediately if a battery is hot to the touch or swelling.
  • Sustained high temperature in an enclosed enclosure can shorten component life. Ensure adequate ventilation in weatherproof enclosures, particularly if the device will be in direct sun.

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