The formula
Runtime in hours = battery capacity in mAh x usable share / average current in mA.
The usable share accounts for the battery not delivering its full label capacity: voltage regulators waste some energy, cold weather cuts capacity, and the board shuts down before the cell is empty. 80 to 90% is a fair starting point for a new lithium cell at room temperature. Use less for cheap cells with optimistic labels and for winter.
Measured current draw
These are documented measurements from makers and users. Conditions differ, so treat them as a range rather than a promise.
| Device | Mode | Average current | Conditions |
|---|---|---|---|
| Heltec Mesh Node T114 (Rev 2.0) | deep sleep | 0.011 mA | Maker page: 'Deep Sleep ~11uA' (not Meshtastic firmware state) Heltec Mesh Node T114 |
| Heltec Mesh Node T114 (Rev 2.0) | tracker mode sleep | 0.022 mA | Maker page: 'Tracker mode sleep ~22uA' Heltec Mesh Node T114 |
| Heltec Mesh Node T114 (Rev 2.0) | Meshtastic low-power mode | 0.023 mA | Maker page: 'current is only 23uA' in Meshtastic low-power mode (exact settings not given) Heltec Mesh Node T114 |
| Heltec Mesh Node T114 (Rev 2.0) | active, GPS off, screen off | 9 mA | Maker page 'GPS OFF, TFT OFF ~9mA' Heltec Mesh Node T114 |
| Heltec Mesh Node T114 (Rev 2.0) | active, GPS off, screen on | 20 mA | Maker page 'GPS OFF, TFT ON ~20mA' Heltec Mesh Node T114 |
| Heltec Mesh Node T114 (Rev 2.0) | active, GPS on, screen on | 51 mA | Maker page 'GPS ON, TFT ON ~51mA' Heltec Mesh Node T114 |
| Heltec WiFi LoRa 32 V4 | low power (unspecified) | 0.02 mA | Maker page: 'Low power consumption is less than 20uA' (max; mode/conditions not stated) Heltec WiFi LoRa 32 V4 |
| Heltec Mesh Node T096 | sleep | 0.012 mA | Meshtastic docs device page: 'about 12 uA sleep current' Meshtastic docs: Heltec Mesh Node T096/T1 |
| deep sleep (Heltec Mesh Node T1, not in devices.json) | 0.011 mA | Meshtastic docs: 'about 11 uA deep-sleep' Meshtastic docs: Heltec Mesh Node T1 | |
| RAK WisBlock Meshtastic starter (RAK19007 + RAK4631 + GPS) | LoRa TX @20 dBm (RAK4631 module only) | 125 mA | RAK4631 datasheet table, PA_BOOST, BT sleep; page text renders '12 5mA' - value read as 125 mA, check PDF before publishing RAK4631 datasheet |
| RAK WisBlock Meshtastic starter (RAK19007 + RAK4631 + GPS) | LoRa TX @17 dBm (module only) | 92 mA | RAK4631 datasheet, BT sleep RAK4631 datasheet |
| RAK WisBlock Meshtastic starter (RAK19007 + RAK4631 + GPS) | LoRa RX @37.5 kbps (module only) | 17 mA | RAK4631 datasheet, BT sleep RAK4631 datasheet |
| RAK WisBlock Meshtastic starter (RAK19007 + RAK4631 + GPS) | BT TX @4 dBm (module only) | 9 mA | RAK4631 datasheet, LoRa sleep RAK4631 datasheet |
| RAK WisBlock Meshtastic starter (RAK19007 + RAK4631 + GPS) | sleep (module only) | 0.002 mA | RAK4631 datasheet: 2.0 uA, LoRa and BT sleep RAK4631 datasheet |
| SX1262 chip RX, LoRa 125 kHz, boosted, LDO | 10.1 mA | Semtech datasheet Table 3-5 (chip only, not a device) Semtech SX1261/2 datasheet Rev 1.2 | |
| SX1262 chip RX, LoRa 125 kHz (DC-DC, VBAT 1.8 V) | 8.2 mA | Semtech datasheet IDDRX row (chip only) Semtech SX1261/2 datasheet Rev 1.2 |
Typical setups
- Pocket node with a phone connection: a nRF52 handheld with a 1,000 to 3,000 mAh cell usually lasts several days between charges, far longer than an ESP32 board with the same cell.
- Fixed node on solar: size the battery for three or more days without sun and use a low-power board.
- Car node: power it from USB and ignore the battery maths; just make sure the node survives heat.
What drains the battery
- The chip family. ESP32 boards keep a power-hungry processor and radio stack awake. nRF52 boards can sleep between packets, which is why they last days or weeks instead of a day or two. See ESP32 vs nRF52.
- Bluetooth and the screen. A phone connection and an always-on display add current. Screen timeout and turning Bluetooth off on a node you don't carry both help.
- GPS. A GPS receiver searching for satellites draws a lot. Set a long position interval or turn GPS off on fixed nodes.
- Role and traffic. A node that repeats every packet on a busy mesh transmits more often. Transmitting is the single most expensive thing a LoRa radio does.
Questions people ask
How big a battery for a solar repeater?
Size the battery to survive several dark days without sun, then size the panel to refill it in one good day. With a low-power nRF52 node the numbers stay small. The steps are in the solar node build guide.
Can I trust the mAh printed on a cheap 18650?
Often not. Unbranded cells sold with "9900 mAh" labels are far below that: real 18650 cells top out around 3,500 mAh. Buy named cells (Samsung, LG, Molicel, Panasonic) from a reputable shop.
Sources
Specs and prices were checked on the dates shown. Prices change often: check the shop before you buy.
- Meshtastic: power configuration - 2026-11-05
- Device measurements: linked in the table above - 2026-11-05
- Battery University: how to define battery capacity - 2026-11-05