An excellent way to clean battery contacts that are not too corroded is white vinegar. It will bubble and eat up the blue salt-like residue that is left behind from leaking alkaline batteries. If you cannot remove the battery contacts from the battery compartment and are worried about getting the vinegar inside the device, you can soak a paper towel and press it up against the battery contact repeatedly until it is cleaned.

Be careful of the skinny ribbon cable on the left (connects the motherboard to the 3.5mm audio jack board). It doesn’t have a lot of slack and is hidden under a piece of foam strip, and if you lever the motherboard too high when trying to pull the battery out, you could damage it or the ZIF connector.

It is easiest to just remove the forward-facing camera board by taking out its two screws, after unplugging the ribbon cable. Trying to hold back the ribbon cable out of the way enough to lever up the motherboard later risks damage to said ribbon cable, and makes moving that corner of the motherboard more difficult.

NOT A NECESSARY STEP! Even with a fairly swollen battery, it can be carefully worked out from the right or left side. You will have to remove all of the motherboard screws to be able to lift it enough to do this, though.

Still missing a circled screw (you can see the empty hole in the image) — there are four along the motherboard under the battery cells. One at each inner corner of the battery, and one towards the middle of the cell inside copper tracing. The photo does not have the right-side one circled; additionally, this one is initially hidden under a piece of foam strip, so be sure not to miss this one!