I recently bought a 2nd hand Gameboy Advance with several cartridges. Problem is it doesn't save any game at all. It kinda gets resetted whenever I save and quit. You have any idea?

I'm no expert, but those save are made on the cardridges, there is no "game boy memory". So those games might be broken. Maybe they are counterfits, those were -very- common during GBA times.

think the gba games had a memory (in the cartrige), maybe they are empty ?

I just opened up Super Mario World 2 and saw it has a clock battery like you said. It's dead I guess, now I need to finish it in one go. Challenge accepted!

or, you know, change the battery ;)

I don't think I can find that easily here.

What kind of battery is it? A standard button cell? You should be able to pick one up at any watch shop or possibly even from a supermarket.

This is not mine but it's the same.

That type of battery isn't too difficult to replace, you need a soldering iron though.

From what I saw online, the battery type is on the circuit board and can be CR2025 or CR2032. But yes, a soldering iron is needed, from what I read, too.

With my technical aptidue, this post looks like:

That type of battery isn't too difficult to replace, you need a particle accelerator though.

are you sure? I know I changed the battery in one of my GBC games without one.

So, not an Fe who works in the military?

So get it to a friend who knows soldering? Someone near you ought to know, especially if they have a garage or mechanic or electronics workshop. (Mot that mechanics need any soldering, but no mechanic today can get anywhere without at least a rudimentary electronics knowledge).
For that battery, yes. Your game might be different and use a battery holder instead of a solder-on battery (though why they'd use that if they didn't think the user would be replacing the battery is an interesting question).