Snowbird 18650
Raw cylindrical cells, the cheapest capacity there is, made safe.
The Feather 1S blocks on a longer board with an 18650 holder. One or two cells in parallel, the thermistor pressed against the cell, and everything else identical: same pinout, same library, same Bluetooth.
- 1S1P or 1S2P 18650 in an on-board holder; LiFePO4 or Li-ion
- Thermistor pad against the cell, so the charge window is the cell's
- 10 W from solar, 15 W from USB-C
- Months per charge at typical IoT duty cycles
$64.00 CAD
Bare board, no cell. Pinout card and compliance insert included.
Shipping from $9.95 CAD in Canada, tracked. US orders ship duty prepaid. Also on Tindie. Ten or more? Ask about wholesale.
Specifications
18650, in numbers
Values marked measured come from the characterization report of 14 September 2026.
Battery
| Cells | 1S, one or two 18650 in parallel |
|---|---|
| Chemistries | Li-ion, LiHV, LiFePO4, LiSOCl2 primary mode |
| Battery interface | On-board 18650 holder with NTC pad; 3-pin JST-PH also fitted |
| Protection | Overcharge, overdischarge, overcurrent, short circuit, temperature; programmable per chemistry |
| Fuel gauge | State of charge, voltage, current, temperature, time to empty; ±3 % on LiFePO4 after one cycle measured |
Inputs
| USB-C | 5 V at 0.5, 1.5 or 3 A, read from the CC lines |
|---|---|
| Solar | 6 to 22 V, MPPT, 10 W continuous, 15 W peak measured |
| Charge current | 50 mA to 3 A in 10 mA steps; default 0.5 C |
| Charger efficiency | 94 % peak, 91 % at 3 A measured |
Outputs
| 3.3 V rail | 1.5 A continuous measured |
|---|---|
| 5 V rail | 2 A continuous, switchable; off by default measured |
| Signals | PG, CHG_DONE, INT, EN5V on jumpered Feather positions; VSYS and VBAT on pads |
Supervisor
| Supervisor | nRF52840 module, Zephyr firmware, I2C at 0x36 |
|---|---|
| Bluetooth LE | BTHome v2 broadcast, Battery Service, custom GATT; read-only by default |
| Idle current | 28 µA outputs unloaded; 42 µA advertising every 2 s; 3 µA in ship mode measured |
| Libraries | Arduino, C, MicroPython; one register map, v1.2 |
Physical
| Outline | Feather-width, 75 × 23 mm, Feather header on one end, four mounting holes |
|---|---|
| Board | 4-layer, ENIG, matte navy |
| Operating temperature | −40 to 85 °C board |
Feather header
| Position | Signal | Direction | Note |
|---|---|---|---|
| 3V | 3V3 | out | Regulated 3.3 V; drives the host's 3V position |
| EN | EN (host) | out | Pulled low through a jumper closed by default, so the host's own regulator stays off |
| BAT | — | — | Not connected, by design: the host's charger must never see the battery |
| USB | — | — | Not connected, so two 5 V sources are never in parallel |
| 11 | INT | out, open drain | Event interrupt; jumper open by default |
| A2 | PG | out, open drain | Power good, both rails in regulation; jumper open by default |
| A3 | CHG_DONE | out, open drain | Charge complete; jumper open by default |
| A5 | EN5V | in, pulled up | Enable the 5 V rail; jumper open by default |
| SDA, SCL | I2C | — | Qwiic bus at 3.3 V; the supervisor answers at 0x36 |
| GND | GND | — | |
| off header | 5V | 2-position 3.5 mm screw terminal block and a pad | Rated 2 A; switched by EN5V and set5V() |
| off header | VSYS | Pad and castellation | Raw system rail, battery or input, whichever the power path selects |
| off header | VBAT | Pad and castellation | Battery terminal after the BMS switch; never the host's BAT position |
| off header | NTC | Battery connector pin 2 and a pad | 10 kΩ, B = 3435 by default; other B values are a setting |
The full map, with the host positions each jumper uses and why, is on the pinout page.
The rest of the line
Same pinout, different battery.
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