Part of the RC Airplane Troubleshooting Center
What I check first: When a LiPo will not start charging, never finishes balancing, or makes the charger throw an error, the charger is usually telling you that something does not agree. The problem might be a setting, a damaged balance lead, a poor main connection, or a cell that is no longer healthy. I do not keep pressing Start until the warning goes away. I stop and find out what the charger is seeing.
Quick Answer
Verify LiPo balance-charge mode, the pack’s cell count, charge current, main-lead polarity, and balance-lead connection. Then compare the charger’s displayed cell voltages. A cell that is dramatically lower than the others, missing from the display, or unable to hold voltage can indicate a damaged lead or unsafe pack.
What Usually Causes This Problem
| Possible cause | What it looks like | What to do |
|---|---|---|
| Wrong charger mode or cell count | The charger reports a cell-count mismatch or refuses to begin | Stop and select the chemistry and cell count printed on the pack |
| Loose or damaged balance lead | A cell disappears, jumps in voltage, or changes when the lead moves | Inspect the plug, wires, and charger balance board; repair only if you are qualified |
| Poor main connection | The charger reports connection break, reverse polarity, or abnormal resistance | Inspect the connector, adapter, solder joints, and polarity |
| Cell imbalance | One cell remains noticeably different while the others reach full voltage | Allow a normal balance cycle only if the pack is undamaged and the difference is modest |
| Failed or deeply discharged cell | A cell reads extremely low, will not recover, or the pack heats during charging | Stop using the pack; do not force-charge or bypass the charger warning |
| Charger or power-supply fault | Known-good packs show the same error | Check charger input power, leads, balance board, firmware, and the manufacturer’s instructions |
Work Through It in This Order
- Read the complete charger message. Write down the exact warning rather than reducing every message to “it won’t charge.” A cell-count error, reverse-polarity warning, connection break, and balance-port error point in different directions.
- Inspect the pack before connecting it. Look for puffing, dents, punctures, damaged insulation, loose connectors, pulled balance wires, discoloration, or an unusual smell. Physical damage ends the test.
- Check the settings against the label. Use the correct battery chemistry and cell count. A normal conservative starting rate is 1C when the battery manufacturer permits it: 2.2 amps for a 2200 mAh pack.
- Compare the cell voltages. Use the charger’s cell monitor or an appropriate cell checker. The cells should be reasonably close. Do not try to rescue a severely low cell with a non-LiPo program or an improvised charging method.
- Eliminate the easy connection problems. Try a known-good charge lead and the correct balance board. Avoid stacks of adapters. Inspect both sides of every connection for backed-out pins or heat damage.
- Cross-check one known-good component at a time. A known-good battery can help test the charger, and a known-good charger can help test the battery. Do not change the charger, leads, power supply, and settings all at once.
- Decide whether the battery is still trustworthy. Retire a pack that is damaged, repeatedly unbalanced, abnormally warm during a normal charge, or unable to hold its cells together. A replacement battery costs less than a burned airplane or shop.
What the Symptom Is Telling You
| What you observe | Where to look next |
|---|---|
| Charger immediately says cell count is wrong | Recheck the selected cell count and inspect whether every cell appears on the balance display. |
| One cell is missing | Suspect the balance plug, a broken balance wire, the balance board, or an internal pack connection. |
| The last part of charging takes a very long time | A modest imbalance can extend balancing, but a cell that repeatedly lags far behind may be deteriorating. |
| Pack becomes warm while charging | Stop. Normal LiPo charging should not make a healthy pack hot. |
| The charger works with every other pack | The evidence points toward that battery or its leads, not a reason to override the warning. |
Change One Thing at a Time
Write down the exact symptom and the conditions that produce it. Make one correction, repeat the same safe ground check or controlled flight test, and compare the result. Changing several settings or parts together may hide the problem without proving what caused it.
Common Mistakes
- Repeatedly restarting the charge without reading the error
- Using NiMH or another chemistry mode to bring up a low LiPo cell
- Charging a damaged pack because its overall voltage looks normal
- Assuming the balance plug is fine because the main connector looks good
- Leaving the battery unattended while testing it
When to Stop and Get Help
Stop troubleshooting alone when the condition can remove control, start a fire, throw a rotating part, or damage the structure. An experienced pilot, engine operator, club safety officer, or the equipment manufacturer can help you test it without turning the next flight into the experiment.
Before the Return-to-Service Flight
- Repeat the complete control-direction and preflight check.
- Use known-good, fully charged power and receiver batteries.
- Choose calm conditions and a large familiar field.
- Keep a clear landing path and climb to a safe altitude before evaluating the correction.
- Land immediately if the original symptom returns.
Related RC Plane Lab Guides
Review LiPo battery charging, storage, and care, choosing an RC battery charger, and a battery or connector that gets hot. Return to the RC Airplane Troubleshooting Center.
RC Plane Lab provides general educational information. Follow the instructions and limits for your specific airplane and equipment.