How to replace Battery contacts?

Alcohol is not what I would use as it won’t cut through the battery corrosion. What you need is white vinegar use a cotton swab (Q-Tip) dipped in the vinegar and hold it against the contacts. You also need to flush the vinegar with water using the same approach using a wet cotton swab.

The bottom contact has a spring to push it up to make contact to the battery if this is not working you’ll need to replace the battery holder. Its a bit of work! Its not something I would recommend for a first timer as its a delicate job. Here’s the Canon A-1 service manual jump down to the exploded views at the end there you’ll see whats involved to get to it. You basically need to take the whole camera apart.