Fault report · batteries

Why the robots shut down mid-movement

A pack with one failed cell charges to green, sits well under 12.6 V, and cuts out the moment the servos pull current. Robot #4 is confirmed; Robot #1 shows the same signature. Every pack is being checked at cell level.

Some robots switch themselves off part-way through moving. The cause is the battery, not the robot. This page shows what was measured on each one.

3S · 11.1 V · 2000 mAh · 10C12.6 V when fullcharger 12.6 V 2 A
0needs replacing
0measured, healthy
6not yet measured
RobotCellsPackWeakestVerdict
#1———not measured
#2———not measured
#3———not measured
#4———not measured
#5———not measured
#6———not measured

A pack is only as good as its weakest cell. Full at 12.6 V; anything under 3.75 V on a single cell while its siblings are full means that pack will charge to green and still cut out under load. Click a robot for its full report.

Capacity is the tank. C rate is the pipe.choosing a replacement

The robot does not fail from running out of charge — it fails when it cannot draw current fast enough. A bigger battery that delivers slowly makes this worse, not better.

max current = C rate × capacity in Ah
ORIGINAL2000 mAh20 A10C — wide pipeBIGGER, BUT SLOWER4500 mAh9 A2C — narrow pipe
Under-rating reproduces the fault

A pack that cannot supply the surge sags under load and browns the controller out — the identical symptom, from a different cause. You would replace the battery and see no change.

What the replacement has to bespecification
PropertyRequiredWhy
Configuration3S · 11.1 V4S is 14.8 V and would destroy the electronics. Never substitute.
Full voltage12.6 VMatches the existing 12.6 V 2 A charger.
Capacity2000 mAh+More is fine if it fits. 80–120 min runtime at stock capacity.
Discharge20 A continuous10C × 2 Ah. The figure that decides whether it works.
ProtectionBMS with balanceCharging runs through the robot's port with no balance lead — the board must be inside the pack.
Port typeCommon portOne 2-pin output does both charge and discharge. A separate-port board has nowhere to connect.
Cells18650 · 65 × 18.5 mmSame cylindrical cells as fitted.

The TonyPi Pro uses the identical pack, so searching that model widens the pool of sellers. support@hiwonder.com will confirm the exact part.

If rebuilding rather than buying
  • Replace all three cells, not just the failed one. A new cell beside two aged ones drifts apart again within months — recreating this exact fault.
  • Spot weld, never solder. Soldering heat damages a cell internally, and a heat-damaged cell fails the way cell 3 did.
  • Reuse the original protection board if it tests good — right rating, right plug, proven with the robot's charging port.
  • New board: 3S, 20–25 A continuous, common port, with balance. Never 10 A — it trips on the servo surge and reproduces the shutdown.

What this means

In short

Batteries are wear items — they age whether used or not, and a set bought together tends to fail together.

Gallery

6 photos