- Garden
- Cordless garden tools
Red LED continuous lighting
Bosch 36V Red LED continuous lighting on garden tool: temp
Risk level
Low
Usually safe to check without specialist tools.
Urgency
Low
Quick answer
On the Bosch AL 36V-20 charger with GBA 36V battery packs (AdvancedGrassCut 36 and AdvancedChain 36V-35-40), continuous lighting of the red LED indicator signals a battery temperature below 0 °C or above 45 °C (battery charging control allows 0 °C to 35 °C). Once in range, rapid charging starts.
Safety first
Stop and check this first
- Store the machine and battery only between -20 °C and 50 °C (never leave the battery in a car in summer or in direct sunlight), never expose the battery or tool to fire or temperatures above 130 °C (risk of explosion), and never spray or immerse the product in water.
- Do not continue to press the On/Off switch after an automatic shut-off of the product by the Electronic Cell Protection (ECP) circuit, as the battery could become damaged.
Safe checks you can perform
- Leave the battery in the AL 36V-20 charger until it reaches the charging range (0 °C to 35 °C)
- Listen for the Active Air Cooling fan (> 30 °C) and clean the venting slots
- Allow the battery to cool or warm to the operating window stated for your tool model
Leave these tasks to a qualified professional
- Do not attempt this professional task: Replacement of a used GBA 36V battery pack if working period after charging is very short
- Do not attempt this professional task: Inspection of the AL 36V-20 charger and cooling fan at an authorised Bosch service centre
What a technician must be able to justify
Technician visit
These are the steps they must carry out and show you. Tick them as they work: if steps are skipped, do not accept a part swap.
These are not instructions for opening or handling the equipment yourself. They are the checks that should support a technical conclusion.
Replacement of a used GBA 36V battery pack if working period after charging is very short
What they doWhen the battery charges within the 0 °C to 35 °C range but delivers a significantly reduced working period after charging, an authorised Bosch service provider supplies a Bosch-approved replacement pack.
They must show youall three green LEDs on the replacement GBA 36V battery lighting up continuously when fully charged.
In writingthe replacement GBA 36V battery specification (2.0 Ah, 4.0 Ah or 6.0 Ah) and separate disposal of the used pack.
Inspection of the AL 36V-20 charger and cooling fan at an authorised Bosch service centre
What they doIf continuous lighting of the red LED indicator persists when the battery is at room temperature (+10... +35 °C) or if the AL 36V-20 Active Air Cooling fan is defective, an authorised Bosch service centre checks the charger.
They must show youautomatic switching to rapid charging (flashing green battery charge indicator) and fan operation above 30 °C.
In writingthe diagnostic report for the AL 36V-20 charger and the 10-digit article number on the nameplate.
Before accepting a part or repair
Nothing has been shown yet. Do not accept a part swap based on the code alone.
Follow these steps
Note: Follow the documented order. An error code identifies the affected system, but it does not prove by itself which part has failed.
Leave the battery in the AL 36V-20 charger until it reaches the charging range (0 °C to 35 °C)
- Who:
- you, in a dry enclosed space within the recommended ambient charging temperature.
- How:
- place the charger in a room matching the Recommended ambient temperature during charging row in Technical Data (+10... +35 °C in F 016 L94 557 for AdvancedGrassCut 36; 0... +35 °C in F 016 L81 992 for AdvancedChain 36V-35-40). On the AL 36V-20, as soon as the allowable charging temperature range is reached, the charger automatically switches to rapid charging.
- Result that matters:
- the continuous red LED turning off and the green battery charge indicator flashing for rapid charging.
- If it switches automatically to rapid charging with a flashing green LED:
- only temperature monitoring was active.
- If the red LED stays continuously lit once the battery is at room temperature:
- check the cooling fan and venting slots next.
- Evidence to keep:
- a note of the room temperature and the LED states on both the AL 36V-20 charger and the GBA 36V battery.
Evidence: Bosch AdvancedGrassCut 36 and AL 36V-20 Charger Original Instructions F 016 L94 557 · Bosch AdvancedChain 36V-35-40 Original Instructions F 016 L81 992
Listen for the Active Air Cooling fan (> 30 °C) and clean the venting slots
- Who:
- you, with a soft, clean and dry brush and the battery removed.
- How:
- make sure the ventilation slots of the AL 36V-20 charger are not covered and occasionally clean the venting slots of the battery pack using a soft, clean and dry brush. According to manual F 016 L94 557, when the battery temperature is above 30 °C the integrated fan switches on and generates a ventilation sound.
- Result that matters:
- clear airflow through the charger ventilation slots and battery venting slots.
- If the fan cools the battery and rapid green charging begins:
- heat after operation was normal.
- If the battery is already at room temperature and the solid red light remains:
- check tool operation or contact Bosch service.
- Evidence to keep:
- a photo of the cleaned venting slots on the GBA 36V battery pack and the AL 36V-20 charger.
Evidence: Bosch AdvancedGrassCut 36 and AL 36V-20 Charger Original Instructions F 016 L94 557 · Bosch AdvancedChain 36V-35-40 Original Instructions F 016 L81 992
Allow the battery to cool or warm to the operating window stated for your tool model
- Who:
- you, with the garden tool switched off and the battery removed.
- How:
- if the motor refuses to start on AdvancedGrassCut 36 (where Technical Data row Permitted ambient temperature during operation B) and storage is -20... +50 °C with limited performance at < 0 °C in F 016 L94 557), allow the battery to cool or warm; if the saw chain runs slow or sawing time per charge is too low on AdvancedChain 36V-35-40, the Troubleshooting table in F 016 L81 992 instructs you to allow the battery to warm naturally to room temperature (within battery operating temperature 0-45 °C).
- Result that matters:
- the battery and motor returning to their normal operating temperature without forcing the On/Off switch.
- If normal operation resumes after cooling or warming:
- cut higher grass in steps to avoid overloading the trimmer.
- If the issue persists at room temperature:
- have the battery and charger checked by an authorised Bosch service agent.
- Evidence to keep:
- a note of the exact model article number (3 600 H78 N.. or 3 600 HB8 6..) and the ambient temperature.
Evidence: Bosch AdvancedGrassCut 36 and AL 36V-20 Charger Original Instructions F 016 L94 557 · Bosch AdvancedChain 36V-35-40 Original Instructions F 016 L81 992
Still not solved
If the error persists, stop here. See what the technician must do and show you.
Where this code applies
A code is meaningful only inside the right product and version context.
Primary scope
- System
- Garden
- Brand
- Bosch
- Product type
- Cordless garden tools
Known code variants
- Battery Temperature below 0°C or above 45°C
- Bosch AL 36V-20 luz roja fija
- Bosch AL 36V-20 solid red LED
- Continuous lighting of the red LED indicator
- Luz fija del indicador de carga rojo del acumulador
- Red battery LED lights up Bosch
- Red LED continuous lighting
- Se enciende el LED rojo del acumulador Bosch
- Temperatura del acumulador inferior a 0 °C o superior a 45 °C
What it means
Covers Bosch 36 V (AL 36V-20 and GBA 36V). In F 016 L94 557 (AdvancedGrassCut 36), Battery Temperature below 0°C or above 45°C states that continuous lighting of the red LED indicator means temperature is out of range: Charging the Battery allows charging at 0 °C to 35 °C, while Technical Data sets Recommended ambient temperature during charging to +10... +35 °C and Permitted ambient temperature during operation B) and storage to -20... +50 °C (limited < 0 °C). In F 016 L81 992 (AdvancedChain 36V-35-40), Technical Data sets recommended charging to 0... +35 °C and Troubleshooting cites battery operating temperature 0-45 °C. Other models vary and this LED alone never proves a fault.
Warnings and stop conditions
- Highsource verified
Store the machine and battery only between -20 °C and 50 °C (never leave the battery in a car in summer or in direct sunlight), never expose the battery or tool to fire or temperatures above 130 °C (risk of explosion), and never spray or immerse the product in water.
Evidence: Bosch AdvancedGrassCut 36 and AL 36V-20 Charger Original Instructions F 016 L94 557 · Bosch AdvancedChain 36V-35-40 Original Instructions F 016 L81 992
- Lowsource verified
Do not continue to press the On/Off switch after an automatic shut-off of the product by the Electronic Cell Protection (ECP) circuit, as the battery could become damaged.
Evidence: Bosch AdvancedGrassCut 36 and AL 36V-20 Charger Original Instructions F 016 L94 557 · Bosch AdvancedChain 36V-35-40 Original Instructions F 016 L81 992
Symptoms and causes
Probable causes · in order
- Battery temperature above 35 °C or 45 °C after garden use or sun exposureCommon
The Charging the Battery section in both manuals (F 016 L94 557 and F 016 L81 992) states that temperature monitoring allows charging only between 0 °C and 35 °C, and the AL 36V-20 charger section lights the continuous red LED under Battery Temperature below 0°C or above 45°C.
Evidence: Bosch AdvancedGrassCut 36 and AL 36V-20 Charger Original Instructions F 016 L94 557 · Bosch AdvancedChain 36V-35-40 Original Instructions F 016 L81 992
- Battery chilled below 0 °C (or below the +10 °C recommended ambient in F 016 L94 557)Possible
Although Permitted ambient temperature during operation B) and storage in F 016 L94 557 and Permitted ambient temperature during storage in F 016 L81 992 allow -20... +50 °C (with 5 °C ideal for storage), charging is blocked below 0 °C.
Evidence: Bosch AdvancedGrassCut 36 and AL 36V-20 Charger Original Instructions F 016 L94 557 · Bosch AdvancedChain 36V-35-40 Original Instructions F 016 L81 992
- Dirty venting slots or defective Active Air Cooling fan (> 30 °C) on AL 36V-20Less common
On the AL 36V-20 charger (manual F 016 L94 557), when the battery temperature is above 30 °C an integrated fan cools the battery to the optimal charging temperature; if the fan is defective or vents are covered, charging time is extended.
Evidence: Bosch AdvancedGrassCut 36 and AL 36V-20 Charger Original Instructions F 016 L94 557
Virtual technician
Does Red LED continuous lighting still appear after these checks?
Answer a few questions to narrow down the likely cause and the safest next action. Guidance only - it never replaces a professional.
Sources and technical references
- 1
Bosch AdvancedGrassCut 36 y cargador AL 36V-20 manual original F 016 L94 557
Robert Bosch Power Tools GmbH · 2022 · official_doc
- 2
Bosch AdvancedGrassCut 36 and AL 36V-20 Charger Original Instructions F 016 L94 557
Robert Bosch Power Tools GmbH · 2022 · official_doc
- 3
Bosch AdvancedChain 36V-35-40 manual original F 016 L81 992
Robert Bosch Power Tools GmbH · 2023 · official_doc
- 4
Bosch AdvancedChain 36V-35-40 Original Instructions F 016 L81 992
Robert Bosch Power Tools GmbH · 2023 · official_doc
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