unfortunately the battery charger wont have enough amperage to run the fans, and if they run at all it wont last very long and will most definitly be a potential fire hazard. i wouldnt try it... what you need is a dc power supply. do you know the amperage/wattage of the fans?
in an earlier post i had recommended
using a 12v model train controller to run some pc fans. i believe a larger version of the same maybe what your looking for, though without knowing how much power your fans require its hard for me to make a recommendation....
dc power supplies are pretty common and can be found for many different applications, from computer power supplies, plug in wall adapters, building controls, etc, etc. one thing to remember is your dc power supply needs to be 1/3 bigger than the power you require ex-
your fan pulls 4amps
you have two fans for a total of 8amps
you need a 12amp power supply.
sizing a d/c power supply like this will prevent it from getting too hot and greatly prolong its service life and efficiency...
however for your particular application i think you can find what type and size of power supply and the appropriate model number here:
http://www.altronix.com/index.php?pid=2&model_num=T12175#T12175
i highly recommend altronix power supplies, there reliabliity and variety is supurb and there are very rugged, and most come with replaceable fuses, a nice feature.
just google the model number you need to find a dealer with the right price