Apple iPhone 7 – How to replace the battery

 Remove the two 3.4 mm pentalobe screws on the bottom edge of the iPhone.

Warm up the lower edge of the phone to soften the adhesive holding the display inplace. Allowing the adhesive to warm up before proceeding.

Attach a suction cup to the lower half of the display assembly, just above the home button.
Be sure the suction cup does not overlap with the home button.

Pull up the suction cup to create a small gap between the display assembly and the rear case.

Insert the flat end of a spudger into the gap.
The watertight adhesive holding the display in place is very strong, and creating this initial gap takes a significant amount of force. 

Slide the spudger to the left along the lower edge of the iPhone.
Twist the spudger to widen the gap between the display and rear case.

Slide the spudger up the left side of the iPhone, starting at the lower edge and moving towards the volume control buttons and silent switch.

Do not try to pry the top edge of the display away from the rear case, as it is held in place by plastic clips that may break.

Remove the spudger from the left side of the iPhone and insert the flat edge into the bottom right corner of the device.

Twist the spudger to widen the gap between the display assembly and the rear case.
Slide the flat end of the spudger up the right side of the phone to break up the adhesive holding the display in place.

Pull up on the suction cup to lift up the display and open the iPhone.

Do not raise the display more than 10 Degree as there are ribbon cables along the right edge of the device connecting the display to the logic board.

Pull up on the small nub on the suction cup to remove it from thefront panel.

Slide an opening pick along the top edge of the iPhone, between the rear case and front panel, to break up the remaining adhesive holding the screen in place.

Pull the display assembly slightly away from the top edge of the phone to disengage the clips holding it to the rear case.

Open the iPhone by swinging the display up from the left side, like the back cover of a book.
Don't try to fully separate the display yet, as several fragile ribbon cables still connect it to the iPhone's logic board.
At this point you may lay the phone down on a flat surface like an open book.

Remove the following tri-point Y000 screws from the lower connector bracket:

Three 1.2 mm screws (RED)
One 2.4 mm screw (ORANGE)
Remove the lower connector bracket.

Use the point of a spudger to lift the battery connector out of its socket on the logic board. Bend the connector cable up slightly to prevent it from making contact with the socket and providing power to the phone.

Use the flat end of a spudger or a fingernail to disconnect the two lower display connectors by prying them straight up from their sockets on the logic board.

To re-attach press connectors, press down on one end until it clicks into place, then repeat on the other end. Do not press down on the middle. If the connector is even slightly misaligned, the connector can bend, causing permanent damage.

Remove the two 1.3 mm Phillips screws securing the bracket over the front panel sensor assembly connector.

Remove the bracket.

Disconnect the front panel sensor assembly connector from its socket on the logic board.

This press connector should also be reconnected one end at a time to minimize the risk of bending.

Remove the display assembly.

Remove the two 1.9 mm Phillips screws securing the barometric ventto the rear case.

Remove the vent.

Use the flat end of a spudger to disconnect the Taptic Engine connector from its socket on the logic board.

Remove the three 1.6 mm Phillips screws securing the Taptic Engineto the rear case.

Remove the Taptic Engine.

Use a pair of tweezers to peel back one of the adhesive strips on the lower edge of the battery.

Use a pair of tweezers to peel back the other adhesive strip on the lower edge of the battery.

Try to keep the strips flat and unwrinkled during this procedure; wrinkled strips will stick together and break instead of pulling out cleanly.
Slowly pull one battery adhesive tab away from the battery, toward the bottom of the iPhone.
Pull steadily, maintaining constant tension on the strip until it slips out from between the battery and the rear case. For best results, pull the strip at a 60 Degree angle or less.
The strip will stretch to many times its original length. Continue pulling and re-grab the strip near the battery if necessary.

Hold down the battery as you remove the second strip, or the strip may fling the battery when it separates from the case.

Otherwise, if either of the adhesive strips broke off underneath the battery and could not be retrieved.

Warm up the rear case, After about a minute, flip the phone over and use a plastic card to break up any remaining adhesive behind the battery.

Do not insert the card from the right, as prying against the logic board can damage it. Also, be sure to not bend the battery.

Don't pry under the topmost section of the battery, near the volume up button and mute switch, or you may damage the volume controls ribbon cable, which is adhered to the rear case just beneath the battery.