The most likely cause of slow charging after borrowing a charger is that the borrowed adapter is not the correct wattage or is not fully compatible with the laptop. Many laptops will still charge with an underpowered or non-matching adapter, but they often charge very slowly, may display a warning like “plugged in, not charging fast,” or may reduce performance to stay within the available power budget. In CompTIA A+ Core 1 troubleshooting, the first step is to check the simplest and most probable cause, especially when the symptom began immediately after a change. Using the proper manufacturer-recommended charger (correct voltage/amperage and connector type, or correct USB-C PD wattage profile if applicable) restores normal charging behavior in most cases.

Adjusting battery performance settings might reduce power draw but does not address the root cause of insufficient charger output. Trying a different charging port can help if a port is damaged, but the timing strongly points to the borrowed charger. Replacing the battery is the most invasive and least likely first step because the battery was presumably functioning before the charger change. Therefore, the technician should first use a different, known-good power supply with the correct specifications.