Begin by powering off your OnePlus Nord N300 5G completely. Use the SIM card ejector tool to remove the SIM card tray from the device. This will prevent any damage to the SIM card and ensure that the phone is completely turned off.

Use a plastic opening tool to gently pry around the edges of the back cover. Start from a corner and work your way around until the cover is completely detached. Be patient and careful to avoid cracking the cover.

Once the back cover is removed, locate the battery connector on the motherboard. Use a spudger to carefully disconnect the battery connector from the motherboard. This step is crucial to prevent short circuits while you work.

Gently lift the battery out using the plastic card or a spudger. If the battery is adhered strongly, use the plastic card to cut through the adhesive. Be cautious not to puncture the battery.

Place the new battery in the compartment, ensuring it is properly aligned. Connect the battery connector to the motherboard. Use adhesive strips or double-sided tape to secure the battery in place, if necessary.

Align the back cover with the phone and snap it back into place by applying gentle pressure around the edges. Ensure all clips are engaged and the cover is flush with the rest of the phone.

Insert the SIM card tray back into the phone. Power on the device to ensure the new battery is functioning correctly. Monitor the charging and battery status to confirm the replacement was successful.