most "cheaper" chargers will take up to 12 hours to properly charge up the battery. THere are other chargers that attempt to fast charge it but I prefer the slower ones.
if it's a servicable battery I like to remove it , clean off dust/dirt off it , remove the top two inspection covers , if it's low then fill it to proper level with distilled water (has to be distilled !!! and you fill it so everything inside it is submerged , no parts should be above water), also be SURE that nothing gets inside the battery , no dust , dirt etc... or it will ruin it. Then I let it charge until it's charged up , with my charger that is about 8-12 hours and you will see it bubbling at the end, hence why I remove the top covers otherwise you're building up pressure inside and I've seen some batteries expand and end up round from too much pressure inside, I Guess they can burst as well but I've never seen that happen.
then slap the covers back on and put it back in the car...
or the easier method is to jump start the car by cables and drive it for a while , that should charge it up as well. Only problem is that if it's the battery that sat for that long then it may be dead , bring it to autozone and they will test it for you.