Chances are it's the battery thats had it and won't hold it's charge . Just have a check that nothing electrical is staying on when it shouldn't be ( ie boot light glovebox light ect). You need to get the battery drop tested and check that the alternator is supplying above 13v . I think halfrauds should beable to test both for you for a small fee if not for free. I assume the battery light isn't on all the time ever when the engine is running ?