Snowbird Pack
2S to 4S packs with balancing, for robots and anything above 5 V.
The multi-cell board. An RC-style pack on XT30 with a JST-XH balance lead, or raw cells on screw terminals, with a balancing BMS and the full 20 W from solar. Double-width Feather, Feather header on one edge.
- 2S, 3S or 4S by a resistor; passive balancing at 50 mA
- 20 W continuous from solar, 15 W from USB-C
- Per-cell voltage and imbalance in the register map
- LTO and sodium-ion packs supported in the charge-voltage range
$89.00 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
Pack, in numbers
Values marked measured come from the characterization report of 14 September 2026.
Battery
| Cells | 2S, 3S or 4S, set by a resistor |
|---|---|
| Chemistries | Li-ion, LiPo, LiHV, LiFePO4, LTO, sodium-ion |
| Battery interface | XT30 and 4-pin JST-XH balance, or 2-position screw terminals for raw cells |
| Protection | Per-cell overcharge and overdischarge, overcurrent, short circuit, temperature; passive balancing |
| Fuel gauge | State of charge, per-cell voltage, imbalance, current, temperature, time to empty measured |
Inputs
| USB-C | 5 V at 0.5, 1.5 or 3 A, read from the CC lines; 15 W into the pack |
|---|---|
| Solar | 6 to 22 V, MPPT, 20 W continuous measured |
| Charge current | 50 mA to 3 A in 10 mA steps; default 0.5 C |
| Charger efficiency | 94 % peak measured |
Outputs
| 3.3 V rail | 1.5 A continuous, synchronous buck measured |
|---|---|
| 5 V rail | 2 A continuous, synchronous buck, switchable; off by default measured |
| Signals | PG, CHG_DONE, INT, EN5V on jumpered Feather positions; VSYS and VBAT on pads and screw terminals |
Supervisor
| Supervisor | nRF52840 module, Zephyr firmware, I2C at 0x36 |
|---|---|
| Bluetooth LE | BTHome v2 broadcast, Battery Service, custom GATT with per-cell voltages; read-only by default |
| Idle current | 31 µA outputs unloaded; 45 µA advertising every 2 s; 4 µA in ship mode measured |
| Libraries | Arduino, C, MicroPython; one register map, v1.2 |
Physical
| Outline | Double-width Feather, 50.8 × 45.7 mm, Feather header on one edge, 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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