badsocref

My 2000 Outback has recently been acting like it has a bad battery (or bad leads). Sometimes I turn the key and just get a click, sometimes I get a couple of slow engine turns, sometimes it starts up just fine. I have checked the battery and leads and they seem fine. If I get a click, and try several more times, the car will eventually start. It will sometimes run for days/weeks with no trouble, but I think it's slowly getting worse. I took it in for service recently, but they could find nothing wrong (I'm guessing it was starting just fine that day). I'm looking for ideas as to what might be wrong. Thanks in advance.