Stihl charger flashes green then red, fan does not start, battery good

User question

Have you resolved it? The same here. For sure my battery itself is good as I checked it elsewhere. The charger flashes with green light and then follows with red. Radiators won't start.

Artificial Intelligence Response

Direct answer to the question

Yes — based on your symptoms, the fault is most likely in the charger, not the battery.

Why:

• You already verified the battery works elsewhere.
• The charger shows a startup indication, then goes to fault.
• The cooling fan you call the “radiators” does not start, which strongly suggests the charger is failing its internal check or has a fan/control fault.

Most likely causes:

• Dirty, oxidized, or bent charger/battery contacts
• Fault on the small sensing / communication pins
• Failed or blocked internal cooling fan on higher-power AL chargers
• Internal charger electronics fault

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Detailed problem analysis

A Stihl charger does not simply apply voltage to the battery. It normally performs a sequence like this:

1. Power-up / self-test
2. Battery detection
3. Temperature / identification / communication check
4. Charge-stage enable
5. Fan enable if required by model and temperature/load

If you see green first, then red, that usually means:

• the charger is receiving mains power,
• the control logic starts,
• then it detects a condition that makes charging unsafe or impossible.

Since your battery is known good on another charger or tool, the diagnosis shifts heavily toward the charger side.

Why the non-starting “radiators” matter

I assume by “radiators” you mean the charger’s cooling fan or airflow system.

On models such as the more powerful Stihl AL chargers, the fan is part of the protection system. If the charger:

• cannot start the fan,
• detects the fan is blocked,
• or does not see the expected electrical response from the fan circuit,

it may abort charging immediately and indicate a fault.

Most probable fault ranking in your case

Suspected issue	Probability
Bad contact / dirty terminals / bent pin	High
Charger internal fault	High
Fan failure or blocked fan	Medium-High
Battery temperature issue	Medium-Low
Battery defect despite “good elsewhere”	Low

Important correction to some common advice

A lot of generic online advice mixes together:

• battery LED meanings,
• charger LED meanings,
• and even non-Stihl charger behavior.

For your case, the single strongest diagnostic fact is this:

A known-good battery + charger starts then faults + fan does not run = charger-side problem is most likely.

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Current information and trends

Modern cordless-tool chargers increasingly use:

• battery ID / BMS interaction
• temperature monitoring
• fan supervision
• fault lockout during startup

So even if a battery can run a tool, a charger may still reject charging if:

• the temperature-sense path is open,
• the communication contact is bad,
• or the charger’s own protection circuit detects a defect.

This is consistent with current charger design trends across Stihl and similar professional battery ecosystems: the charger is intentionally conservative and will refuse operation on even a minor sensing fault.

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Supporting explanations and details

1. Contact fault

This is the easiest and most common issue.

The charger usually has:

• two main power contacts,
• and one or more smaller contacts for sensing/communication.

If the small pin is dirty, recessed, or bent:

• the battery may still physically fit,
• but the charger cannot validate it,
• so it throws a fault.

2. Fan fault

If your charger model has active cooling:

• a jammed fan,
• dead fan motor,
• disconnected fan,
• or failed fan driver transistor

can stop the charger completely.

The charger may never proceed to charging current if it thinks cooling is unavailable.

3. Internal power/control fault

A charger can power its LED logic but still fail in the actual charging section. In practice this can mean:

• failed low-voltage auxiliary supply,
• damaged control board,
• failed MOSFET / switching stage,
• bad capacitor,
• or failed thermal sensor.

That matches the symptom “looks alive, but immediately faults.”

4. Temperature-related rejection

This is still possible, but less likely if:

• the same battery works elsewhere,
• and the problem is repeatable only on this charger.

Still, if the battery is very cold or very hot, let it stabilize at room temperature before retesting.

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Ethical and legal aspects

• Do not open the charger unless you are qualified to work on mains-powered switch-mode power supplies.
• These chargers contain hazardous voltages and capacitors that may remain charged after unplugging.
• Opening the case may also void warranty.
• If this is a work tool, the safest path is often authorized service or replacement, because battery-charger safety systems are designed to prevent overheating and fire risk.

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Practical guidelines

What to do first

1. Unplug the charger
2. Remove the battery
3. Inspect all charger contacts and battery terminals
4. Clean with:
   • isopropyl alcohol,
   • lint-free swab or soft brush
5. Check for:
   • bent pins,
   • recessed pins,
   • corrosion,
   • sawdust, sap, dirt

Then do a reset

1. Leave charger unplugged for 10–15 minutes
2. Reconnect power
3. Insert battery again firmly

Then isolate the fault

• Test the charger with another known-good battery
• If it behaves the same way, the charger is defective
• If another battery charges normally, then your first battery may have a marginal sensing issue even if it works elsewhere

If your model has a fan

Look through the vents:

• check whether the fan is physically blocked by dust/debris
• do not insert metal tools into the vents
• use low-pressure air only if you know what you are doing

What not to do

• Do not bypass the sensing pins
• Do not “jump start” the battery with random power sources
• Do not continue cycling a faulting charger unattended

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Possible disclaimers or additional notes

• The exact meaning of the LEDs can vary a little by charger model: AL 1, AL 101, AL 301, AL 300, AL 500, etc.
• “Radiators” is not standard terminology here, so I am assuming you mean the cooling fan.
• If it is an AL 101, fan-related diagnosis is less relevant than on higher-power chargers.
• If it is an AL 300 / AL 301 / AL 500-type unit, the non-starting fan becomes a much stronger clue.

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Suggestions for further research

To narrow it down further, the most useful next data would be:

• Exact charger model
• Exact battery model
• Whether the charger shows:
  • steady green,
  • flashing green,
  • steady red,
  • flashing red,
  • or alternating sequence
• Whether the battery charges on another Stihl charger
• Whether the fan ever twitches at startup

If you can provide that, a much more precise diagnosis is possible.

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Brief summary

Your description points to a charger fault, not a battery fault.

Most likely explanation:

• the charger powers up,
• fails its safety/startup check,
• and stops before charging begins.

First actions:

• clean and inspect the contacts,
• check for bent sensing pins,
• reset the charger,
• test with another known-good battery.

If the symptom stays the same, especially with no fan activity, the charger is very likely defective and should be serviced or replaced.

If you want, send me the exact Stihl charger model and I can give you a model-specific fault interpretation and next test steps.

Disclaimer: The responses provided by artificial intelligence (language model) may be inaccurate and misleading. Elektroda is not responsible for the accuracy, reliability, or completeness of the presented information. All responses should be verified by the user.