When collecting older games —or simply revisiting your childhood games— it's usually a good idea to clean the games and, ideally, replace their batteries. A few months ago I made a video about the first Super Famicom game I replaced the battery of, but I had more work ahead of me.
Several weeks ago I wasn't feeling too well, and instead of sitting around doing nothing I wanted to try to spend my time in a more useful way, and see how far I could get with replacing batteries, as-well as actually cleaning the contacts of the game cartridges. Several of the games I have had a lot of trouble starting up, so I often had to fiddle with them quite a bit before they would actually boot.
Oddly enough, replacing the batteries ended up being the least time consuming part. I originally anticipated that taking quite some time, but even with my very basic soldering iron and absolutely zero desoldering tools/gear available, I rather quickly went through and replaced an additional 8 batteries. I ran out of batteries and holders so could not continue, but to be honest after about 4 hours of doing this my neck and back really didn't care to continue either.
Of all the 9 batteries I replaced so far, only one had slight corrosion which, fortunately, was only on the battery itself, leaving the board intact. Most of the batteries actually also still worked, but as these are now at least 25 years old, it is only a matter of time before they kick the bucket, so I went ahead and replaced them now. This way I can comfortably play the games, not having to worry about potentially losing my save-game down the line. Well, for the next 25 years or so, anyway.
Cleaning took more time. I wanted to do it right, so had to slowly work all the pins on both sides of each game cart. I used rubbing alcohol and cotton swabs to do this, and while it took quite some time, the end result couldn't be better; Every single game I cleaned now works the first time I insert them, every time. Awesome!
I highly recommend you at least clean the pins of your games, as the difference is very noticeable and it will help extend the life of your carts as you're not re-inserting them a bunch of times just to get them to work once.
In the end I cleaned about half of my collection, so I've still got more to go. But that's fine. One of the reasons I like getting these games on physical carts is to be able to hold them in my hands, as so much these days is completely digital, so if I need to clean them every now and then, or spend some time soldering, I really don't mind. It's quite meditative, actually.
If you'd like to see the process of replacing a battery on a game cart, and haven't seen it already, I recommend checking out a short video I made on this subject a few months ago: