The one rule that matters most
Deep discharge is the failure you can’t undo. Per Unitree’s official Battery and Charger manual, the pack cuts output at 24 V to protect itself — but a battery left flat in a drawer keeps draining, and the manual is blunt that over-discharge “may cause damage to the battery cell and cannot be restored to use.” A $500 pack dies not from running, but from sitting empty.
Charging rules (from the manual, not folklore)
- Power the battery off and take it out of the robot before charging — the manual requires both, and forbids hot-plugging the pack in or out while it’s on.
- Never charge straight after a run. Forced charging of a hot pack “will seriously damage the life of the battery.” Let it cool to room temperature first.
- Mind the temperature window. The BMS blocks charging below 0°C or above 50°C; Unitree says the ideal charging ambient is 5–40°C and that staying in it “can greatly prolong” pack life.
- Official charger only, within sight, on a non-flammable surface. All LEDs off = full; unplug at that point. The standard charger fills the 8,000 mAh pack in ~2 h; the quick charger (302 W vs 119 W) does it in ~0.8 h.
Storage rules
- The 30% → 70% rule: in long-term storage, check the pack regularly; if it’s under 30%, charge it to 70% before putting it away again. The manual gives no fixed calendar interval — just “regularly” — so put a monthly reminder on your phone.
- Pull the battery out of the robot when not in use; the user manual repeats this for long-term storage (robot back in its case, pack stored separately).
- Keep it at 22–28°C ideally, never in a room above 40°C, away from heat sources, and dry.
- Built-in self-discharge is a feature, not a fault: left above 65% with no use for 10 days, the pack automatically discharges itself to 65%. It takes about an hour, shows no LED activity, and slight warmth is normal. That 65% is also Unitree’s target charge for transporting the battery.
Checking charge without booting the robot
With the battery off, one short press of its button shows charge on the 4-LED bar (each LED ≈ a quarter; 4 solid = 88–100%). If the LEDs flash at 2.5 Hz during charging, the BMS is reporting a protection fault — temperature, voltage, or over-current — not a normal charge cycle.
What replacement costs
Unitree sells the Go2 battery for $500 on its official shop — same price for the standard 8,000 mAh (BT2-05, 1–2 h runtime) and the optional long-endurance 15,000 mAh (BT2-06, 3–5 h). US reseller RoboStore lists both at $560. Chargers are $100 (standard or fast) from Unitree. Two honest gaps in the published data: Unitree publishes no cycle-life figure for the pack, and no separate battery warranty term — and the user manual classes battery aging under normal use as wear Unitree won’t cover. Care is the warranty.