it appears that your charger is the fast charger, 500mah. so youre good there. clean the contacts like mentioned above. use rubbing alcohol to do that.
another key bit of info would be the wall adapter youre using. some wall adapters only put out half an amp, some 1, some 2. using a higher rated wall adapter might help if youre not doing that already.
my chargers are all the 420mah ones. i use 1 amp and 2 amp wall adapters. typically the 1300mah spinner i had would take 4 hours from death, although i rarely let it die. its always best the charge before death to prolong the lifetime of your batts. ideally, you want to charge at 50% to get tip top lifetime. but thats not always practical. i typcally charged after a couple hours of use. but occasionally id let it die from use. cant always be super vigilant.