Miss, are you using junk yard 6V batteries. When you say new do you mean brand new? BTW what brand are they? You could have an inherent electrical leak/draw that you don't know about.... or generator no good. Bad connections at battery or generator. Should check all that ASAP... but free batteries are tempting. 12V conversion is fairly easy.
Here is another issue: Here in AZ, batteries don't last more than about 3 yrs due to heat. That's been true for decades. Canada has real cold/freezing weather right? How do your friend's batteries hold up? If you are a little off on your 2 year estimate, you may be where we are, at 3 years.
