Press and hold the power button, then select 'Power Off' to turn off the device completely. Wait for the screen to go black and all lights to turn off.

Insert a SIM eject tool into the small hole on the SIM tray located on the side of the phone. Apply slight pressure until the tray pops out, then remove it and set it aside.

Use a heat gun or hairdryer to gently heat the edges of the back cover. This softens the adhesive, making it easier to remove. Be careful not to overheat the device.

Use a suction cup to lift the back cover slightly. Insert a plastic opening tool into the gap and carefully work around the edges to release the adhesive. Gently lift the cover off once it's free.

Locate the battery connector on the motherboard. Use a spudger to carefully disconnect it by prying it upwards. This will ensure no power is flowing through the device during the repair.

Using a Phillips #00 screwdriver, remove the screws securing the battery bracket. Carefully lift the bracket and set it aside with the screws in a safe place.

Use the spudger to gently lift the old battery out of the phone. If it's stuck, apply a bit of heat to soften the adhesive further. Take care not to bend or puncture the battery.

Place the new battery in the compartment, ensuring it aligns with the connectors. Press it down gently to adhere it with the new adhesive strips.

Reconnect the battery connector to the motherboard. Replace the battery bracket and secure it with screws.

Align the back cover with the phone and press down firmly around the edges to secure it. Reinsert the SIM tray.

Press and hold the power button to turn the device back on. Ensure the new battery is functioning correctly by checking the charge level and performance.