Kobalt 24V/48V: USB-C Battery Overheating - Diagnosis

⚠️ SAFETY WARNING / FIRE HAZARD. This device contains lithium batteries. Improper piercing or bending during disassembly can cause explosions or flames. Intervention requires precision and the assistance of a specialized technician is recommended. ReeFix provides this diagnosis EXCLUSIVELY for educational and informational purposes.

OBSERVED SYMPTOMS

The main symptom is the abnormal overheating of the Kobalt 24V/48V battery pack, with a potential risk of smoke, sparks, or fire, which specifically occurs when the battery is recharged via the auxiliary USB-C port while it is still inserted (housed) inside the power tool (e.g., KMS 1524-06 string trimmer or other compatible garden tools). You might notice excessive heat to the touch, a burning smell, or in severe cases, deformation of the plastic casing.

WHAT TO EXCLUDE

This analysis excludes the following scenarios, which are not the primary cause of the described problem, but help to narrow down the diagnosis:

• Charging with a traditional external charger: If the battery charges correctly and without overheating using the original slide-in desktop charger (via the main power contacts), the problem is limited exclusively to the integrated USB-C functionality and its electrical interaction with the tool.
• Batteries without a USB-C port: Traditional Kobalt batteries that do not have an integrated USB-C charging port are not affected by this design flaw or the related safety recall.

FINAL CAUSE

Technical evaluation indicates an almost absolute probability of an inherent electrical design defect, officially recognized through a Consumer Product Safety Commission (CPSC) recall.

1. Electrical short circuit due to coupling in the tool (80%)

• Why: When the battery is inserted into the power tool, the simultaneous connection of the USB-C cable creates an unintended electrical path (ground loop or direct short circuit) between the tool's main power terminals and the USB-C charging circuit integrated into the BMS. This causes immediate and uncontrolled overheating, with a severe risk of flames.
• Key signal: Overheating or the presence of sparks occurs exclusively when starting USB-C charging with the battery mounted in the tool.
• Common user error: Ignoring the danger and charging the device via USB-C without removing the battery from the tool's housing.

2. Insufficient thermal dissipation in the housing (15%)

• Why: The enclosed housing of the tool (as in the KMS 1524-06 string trimmer) acts as a thermal insulator. The heat generated by the USB-C charging's DC-DC conversion circuit is not dissipated, accelerating the thermal degradation of the BMS electronic components and cells.

3. Use of non-compliant USB-C power adapters or cables (5%)

• Why: The use of poor-quality or non-Power Delivery compatible chargers can cause instability in the charging voltage, increasing Joule effect losses and aggravating the thermal criticality of the circuit.

Quick checks (for the user)

1. Model code verification: Check if your Kobalt 24V battery has a USB-C port and if your tool is among those recalled (KMS 1524-06 string trimmer, blowers, chainsaws, lawnmowers purchased between January and May 2026).
2. Exclusive use of the slide-in charger: If you need to use the existing battery before receiving a replacement, charge it exclusively via the original slide-in desktop charger. Absolutely do not use the USB-C port.

If you own one of these models, we recommend immediately checking the details of the official recall for the Kobalt 24V USB-C battery. The manufacturer has launched a free replacement campaign to permanently eliminate this serious design flaw.

Output for specialized technician

"The Kobalt 24V battery pack (used in 24V and 48V OPE systems produced by Greenworks) is subject to an official CPSC recall due to a severe risk of short circuit and fire during charging via the integrated USB-C port when the battery is inserted into the tool. The defect lies in the electrical interaction between the tool's power contacts and the USB-C charging/BMS circuit, which generates a return loop or a direct short circuit. During analysis, verify the integrity of the printed circuit board (PCB) and the Power Delivery negotiation chip. Since the manufacturer offers free replacement with batteries without a USB-C port, any attempt at repair or artisanal modification of the BMS is discouraged for safety reasons."

Necessary tools (for technician)

• Professional Digital Multimeter
• Infrared Thermal Camera for Electronics
• Professional Soldering Station
• Kobalt 24V External Charger

Operational decision: Due to the severe risk of short circuit and the official CPSC recall, immediately stop charging the battery via the USB-C port while it is inserted into the tool. Register the product on the official Greenworks/Kobalt website to receive a free replacement with a safe, new-generation battery.