There is no reason why disconnecting the positive cable instead of the ground should drain the battery. An open circuit is the same no matter where the disconnect is made. Have somebody recharge and load test the battery- - - -chances are your "brand new battery" is a brand new piece of junk!

Load test- - - -load the battery to 1/2 the cold cranking amp rating for 30 seconds, then check the battery terminal voltage with the load still on the battery. The voltage should not drop below 9.6 volts. Example: A 550 CCA battery gets loaded to 275 amps for 30 seconds. The specific gravity of the electrolyte should be at least 1.250 in all 6 cells before testing. Full-charge specific gravity should be 1.250-1.265.

Good luck!
Jerry

"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway
Love your enemies and drive 'em nuts!