Me and a friend of mine have the same game cart for gba sp "spyro" his game works strange it does not save the game progres and this is impoetant for this game... we have tedted mine on his gba sp and it works fine. His game on my gba is having the same problem...
Sounds like the battery needs a replacement, right?
I don't know how to check if there is something wrong with the battery
It could be a pirate version, Spyro is pirated a lot but the differences can be hard to see. If you can find the right screwdriver, you can take the cart apart and swap the cell battery if it has one.
Thanks there was a batter inside ( I used a watch battery to replace the old one) and now the save slots works :)