new cartridge battery, game saves, but dissapears after a little while

i have changes battery for a pokemon gold version. the game boots up first time after battery change, starts a new file since there were naturally no save file there. i play for a few minutes, saves the game. turns off gameboy, then turns it on again. the save file is there. i leave it overnight, and no save file. i can still save and turn it off and on to find the file there, it just dissapears after a little while. have anyone encountered this problem before