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:relay. The figures below are approximate community estimates - actual runtime varies widely with screen use, GPS, and transmit duty cycle:
| Device Type | Typical Battery Life | Notes |
|---|---|---|
| ESP32 client node (e.g., Heltec V3, T-Beam) | ~1 - 3 days (approx.) | 3000 mAh battery, moderate messaging. ESP32 nodes are power-hungry; T-Beam with GPS active is toward the shorter end. |
| nRF52 client node (e.g., T114, RAK4631) | ~3 - 7 days (approx.) | Lower power than |
| E-ink display device (T-Echo, Wireless Paper) | ~7 - 14 days (approx.) | E-ink uses power only when updating; excellent for always-on carry |
| Repeater node (always receiving) |
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. Note: this is the discharge range - see the cold-weather note below for the separate, stricter charging limit.
- Safety: LiFePO4 is far more resistant to thermal runaway than LiPo, with a much higher onset temperature (~270°C vs ~150-210°C for LiPo/NMC), so it is much less likely to ignite under abuse. It is not completely immune, however - under severe abuse (puncture, dead short, gross overcharge, or charging a frozen cell) any lithium cell can vent flammable gas, overheat, and in extreme cases ignite. Still use a proper BMS and fusing, and avoid puncture or overcharge. LiPo combusts far more readily under these conditions.
- Cycle life: LiFePO4 typically lasts 2,000 - 5,000+ charge cycles. LiPo lasts roughly 300 -
5001,000 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.
Critical cold-weather note: Do not charge any lithium chemistry, including LiFePO4, below 0°C (32°F) - sub-freezing charging causes lithium plating, which permanently damages the cell and can create internal shorts (a fire hazard on later cycles). For winter solar deployments, use a BMS or charge controller with low-temperature charge cutoff, or a self-heating/insulated battery. Separately, evenLiFePO4 LiFePO4also loses approximatelya 50%large fraction of its usable capacity atin extreme cold (roughly half by around - 40°F (/ - 40°C),C, soas ifa rough estimate) - and note that many LiFePO4 cells are only rated for discharge down to about - 20°C, not - 40°C. If deploying in Minnesota, the Dakotas, Canada, or similar climates, check your cell's datasheet and size your battery bank for worst-case winter temperatures -temperatures, not just rated capacity.
Are cheap 18650 batteries from Amazon OK?
Be very careful. First, for reference: a real 18650 cell holds roughly 2,500 - 3,500 mAh. Treat any listing above about 3,600 mAh as false advertising, regardless of price. The 18650 battery market on Amazon is saturated with counterfeit and significantly overstated-capacity cells.cells A- a cell listed as "9800mAh"9800 mAh" for $3a few dollars is physically impossible - genuine high-quality 18650 cells max out around 3,500 mAh.impossible.
Counterfeit cells often have:
- Actual capacity 20 - 50% of stated capacity
- Poor
safetyprotectioncircuitscircuitry or none atallall. (Note: many legitimate 18650 cells are intentionally sold "unprotected" - bare cells without a built-in protection PCB - which is normal and expected when they are used inside a pack that has its own BMS. The concern with counterfeits is the absence of any protection in a context that needs it, plus generally poor quality control.) - 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.
ForWorked example for a node drawing an assumed ~150 mAaverage:average (your node's actual average draw varies by role and TX duty - measure it if you can): 150 mA × 24 h × 3 daysat=15010,800mAmAh = 10.8 Ah minimum. A 20 Ah LiFePO4 battery provides good margin.
Safety: fuse the battery. Install an appropriately-rated fuse between the battery and the charge controller/load. An unfused lithium bank (especially a 20 - 40 Ah LiFePO4 pack) can deliver very high fault current into a wiring fault or a shorted controller and start a fire; a fuse is standard practice and is not optional.
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
cantypically drop to about 2.5 - 3.5 hours/day (e.g. Minnesota winter is roughly 3 - 5 h/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;overcast push peak sun hours down toward ~2.5 h/day or less in deep winter; plan for 2 - 3 hours/day in winter.day. 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-basedMost devicesESP32 LoRa boards (e.g. Heltec V3, which use the SX1262) transmit at up to about 22 dBm conducted and run slightly warm at 20that level - 27 dBm TX power. Thisthis is not a concern at normal operating temperatures. Higher outputs (27 dBm and above, i.e. 0.5 W) are beyond the SX1262's native ~22 dBm capability and require an external power-amplifier module; a bare Heltec cannot reach them.
Concerns to watch for:
- Excessive heat from the battery area may indicate a failing or improperly charged
LiPolithium battery.Discontinue use immediately ifIf abatterycell is hot to the touch orswelling.swelling, stop charging and disconnect it immediately. Do not puncture, crush, or continue to use a swollen cell - it is a fire and venting hazard. Move it to a non-combustible surface away from flammable material, let it cool, and dispose of it at a battery-recycling or hazardous-waste facility - never in the household trash. - Sustained high temperature
ininsideanaenclosedsealed enclosure can shorten component life.Ensure adequate ventilation inA weatherproofenclosures,boxparticularlyisifby definition sealed, so don't drill open holes (that defeats thedeviceweatherproofing)will-beinsteadinuse vapor-permeable vents (e.g. Gore vents) or a sun shield, and keep the enclosure out of directsun.sun where practical.