Battery drain

Hi,
I bought a 2005 used Jeep Wrangler and it is doing great with the exception that a charge can't be held in its electrical system. I have taken in the Jeep 3 times and spent a total of $1000 and the problem is no better (I only spent $12,000.00 total on buying it). It started immediately after buying it. If you didn't drive the Jeep everyday, the battery would not hold enough charge to start it. I bought a new battery, cleaned and welded the posts, had the alt and gen checked out, and made sure to turn the key all the way to the complete off setting when turning it off, and, of course, the lights are all completely off. I'm getting pretty frustarted, because it can't be relied on to start, unless I put a trickle (2 amp) charger on it every night. I'm sure the guy trading it thought he was really getting something over. And he has to me, to the tune of $1000. I otherwise really like the Jeep, it drives and looks great, do you have any suggestions?