Battery Sizing for LoRa Mesh Nodes Correctly sizing the battery for a solar-powered LoRa node prevents two failure modes: undersizing (the battery dies overnight or during cloudy periods) and oversizing (wasted cost and weight). This page walks through a systematic methodology and provides worked examples for three common node types. Step 1 - Measure Actual Current Draw Never rely solely on datasheet figures. Real-world current draw depends on firmware configuration, peripherals, GPS lock cycles, LoRa transmit duty cycle, and whether deep sleep is used. Measure with a USB power meter (e.g., UM25C, AT34) or an inline current shunt (e.g., INA219 module on the 3.3 V rail). Take measurements in three states: Transmit peak: Current during an active LoRa TX burst (typically 80 - 120 mA at 3.3 V for SX1276-based modules at +17 dBm). Receive / idle: Firmware running, radio in RX mode, no TX. This is the whole-node draw (MCU + radio + regulator + peripherals), typically 30 - 80 mA on ESP32-class boards — the SX1276 radio alone is only ~11 - 14 mA in RX, the rest is the MCU and supporting circuitry. Confirm against a board-level power measurement for your platform. Deep sleep (if used): Microcontroller and radio in lowest power state, highly design-dependent (0.01 - 10 mA). An nRF52840 board with clean power management can reach low microamps, whereas an ESP32 board with a leaky regulator may sit in the milliamp range — measure your specific board (e.g. nRF52840 vs ESP32 T-Beam) rather than assuming. Calculate a weighted average current based on the fraction of time spent in each state. The example below is illustrative, using an assumed duty cycle rather than measured T-Beam data — substitute your own measured currents and duty cycle. For a Meshtastic router node set to 5-minute heartbeat with 20-second sleep cycles: Illustrative example (assumed duty cycle): T-Beam v1.1 (ESP32 + SX1276 + NEO-6M GPS) TX (0.5% of time at 120 mA) = 0.6 mA average RX active (79.5% at 80 mA) = 63.6 mA average Deep sleep (20% at 3 mA) = 0.6 mA average ───────────────────────────────────────────────── Weighted average ≈ 64.8 mA Step 2 - Calculate Daily Watt-Hours Multiply the average current (in amps) by the system voltage and by 24 hours. Use the voltage the node actually runs at when you measured the current — for a single-cell board that is ~3.7 V, even if the battery pack you eventually buy is a 12.8 V LiFePO4 pack. Energy (Wh) is conserved across the voltage conversion: you compute daily Wh at the node's running voltage, then later convert the required Wh to pack Ah using the pack's nominal voltage (Step 6). Do not mix the 3.7 V cell figure with a 12.8 V pack in the same multiplication. Daily_Wh = I_avg(A) × V_system(V) × 24 h Example: 64.8 mA × 3.7 V × 24 h = 5.75 Wh/day If your system runs at 5 V (e.g., USB-powered node) or 12 V (e.g., Raspberry Pi gateway), substitute the appropriate system voltage. Step 3 - Determine Required Autonomy Days Autonomy is the number of consecutive days with no solar input (full cloud cover, snow burial, north-facing shade) the battery must sustain the node. Select based on your climate and criticality: Deployment Type Recommended Autonomy Rationale Sunny desert / Southwest US 3 - 5 days Extended low-sun periods are rare Pacific Northwest / Northeast US 5 - 7 days Multi-day overcast events common Nov - Mar High alpine / polar 7 - 14 days Snow burial possible; winter darkness Non-solar (mains backup only) 0.5 - 1 day Bridge a brief power outage Step 4 - Calculate Raw Battery Capacity Raw_Wh = Daily_Wh × Autonomy_days Example (5 days autonomy): 5.75 Wh × 5 = 28.75 Wh Step 5 - Apply Derating Factors Real batteries deliver less than their nameplate capacity due to temperature, aging, and depth-of-discharge limits. Apply the following derating multipliers. The temperature factors below are conservative planning estimates for a −10 °C average low, not values pulled from a specific datasheet curve — check your battery's own capacity-vs-temperature curve where one is published: Factor LiFePO4 LiPo Lead Acid Max recommended DoD 80% (use 0.80) 80% (use 0.80) 50% (use 0.50) Temperature derating (cold climate, −10 °C avg low — conservative estimate) 0.85 0.70 0.65 End-of-life capacity (design to still work at EOL) 0.80 0.80 0.80 Combined derating factor 0.80 × 0.85 × 0.80 = 0.544 0.80 × 0.70 × 0.80 = 0.448 0.50 × 0.65 × 0.80 = 0.260 Cold-charge warning: Never charge any lithium chemistry — including LiFePO4 — below 0 °C (32 °F); sub-freezing charging causes lithium plating and permanent damage. In cold climates require a BMS with low-temperature charge cutoff or a charge controller with a battery temperature sensor. (LiFePO4 may still discharge down to about −20 °C.) Required_Wh = Raw_Wh / Combined_derating_factor Example (LiFePO4, cold climate): 28.75 / 0.544 = 52.8 Wh → round up to 53 Wh Step 6 - Add a 20% Safety Margin and Convert to Ah Final_Wh = Required_Wh × 1.20 (20% safety margin) Final_Ah = Final_Wh / V_nominal_pack Example (LiFePO4, 12.8 V nominal pack): Final_Wh = 52.8 × 1.20 = 63.4 Wh Final_Ah = 63.4 / 12.8 = 4.95 Ah → use a 6 Ah pack Worked Examples Example A - ESP32 LoRa Repeater (T-Beam, indoor/outdoor enclosure) Platform TTGO T-Beam v1.1 (ESP32 + SX1276 + AXP192 PMIC) Measured average current 65 mA at 3.7 V = 0.240 Wh/h Daily consumption 5.76 Wh/day Target autonomy 5 days (Pacific NW) Raw requirement 28.8 Wh After derating (LiFePO4, cold) 28.8 / 0.544 = 52.9 Wh With safety margin 63.5 Wh → use 6 Ah at 12.8 V (76.8 Wh nominal) Recommended battery Bioenno BLF-1206A (6 Ah, 12.8 V LiFePO4) or equivalent Example B - nRF52840 Ultra-Low-Power Node (RAK4631 + solar harvest) Note on chemistry: the LiPo sizing below is shown only to illustrate the LiPo derating column. For an unattended outdoor or permanent solar deployment, LiPo is not recommended — use a LiFePO4 (or a protected Li-ion) cell instead, per the battery-chemistry, LiFePO4-vs-LiPo, and cold-weather pages. The 8 mA average is an assumed measurement; the duty cycle behind it (mostly deep sleep with brief RX) must be confirmed on your own board. Platform RAK WisBlock Core RAK4631 + RAK12500 GPS (GPS duty-cycled off) Measured average current 8 mA at 3.7 V = 0.0296 Wh/h (assumed, with aggressive sleep — confirm duty cycle on your board) Daily consumption 0.71 Wh/day Target autonomy 7 days Raw requirement 4.97 Wh After derating (LiPo, moderate climate — illustration only) 4.97 / (0.80 × 0.80 × 0.80) = 9.71 Wh With safety margin 11.65 Wh → at 3.7 V = 3.15 Ah → use a 3.5 Ah cell Recommended battery EEMB LP905060 3.7 V 3500 mAh (meets the 3.15 Ah requirement). Note: Adafruit #328 is a 2500 mAh cell — below the 3.15 Ah needed here, so prefer the 3500 mAh option for outdoor use. Example C - Raspberry Pi Zero 2W + SX1302 HAT Gateway Gateway note: a gateway is the highest-value node in an incident (it bridges to internet/MQTT), so the 3-day / no-cold-derate figures below are a desert best-case, not a default. For a gateway, use at least 5-day autonomy even in sunny climates, and do not apply a 1.00 temperature factor unless you have confirmed the battery never sees sub-freezing nights. The 620 mA average is a representative estimate (Pi Zero 2W idles ~150 - 250 mA, the SX1302 HAT adds load) — measure your own build. Platform RPi Zero 2W + RAK2287 SX1302 HAT + LTE modem Measured average current 620 mA at 5 V = 3.1 W = 3.1 Wh/h (representative estimate — measure your build) Daily consumption 74.4 Wh/day Target autonomy 5 days (use ≥5 days for a gateway, even in sunny climates) Raw requirement 372 Wh After derating (LiFePO4: 0.80 DoD × 0.85 temp × 0.80 EOL = 0.544) 372 / 0.544 = 684 Wh With safety margin 821 Wh → at 12.8 V = 64 Ah → use a 100 Ah pack Recommended battery Battle Born BB10012 (100 Ah, 12 V LiFePO4) or 2× EVE LF50K-class packs in parallel Rule of Thumb Quick Reference These figures are computed from the Step 1-6 methodology (5-day autonomy, LiFePO4, with DoD/cold/EOL derate and a 20% margin). They are planning floors — run your own numbers from your measured daily Wh. Node Type Typical Daily Wh Minimum Battery (5-day, LiFePO4) nRF52840 sleepy node 0.3 - 1.5 Wh ~1 - 5 Ah @ 3.7 V ESP32 Meshtastic router (no GPS) 3 - 5 Wh ~7 - 12 Ah @ 3.7 V (or ~2 - 4 Ah @ 12.8 V) ESP32 + GPS always-on 5 - 10 Wh ~12 - 25 Ah @ 3.7 V (or ~4 - 7 Ah @ 12.8 V) Pi Zero 2W gateway 60 - 90 Wh ~50 - 75 Ah @ 12 V Pi 4 + LTE gateway 100 - 150 Wh ~80 - 120 Ah @ 12 V