There's a slight problem with load and conductance testing, as I've discovered. These can only you if the battery has the cranking amps to start the engine.
They tell you NOTHING about the battery's reserve capacity. It's very possible for a battery that has lost 50% of it's reserve capacity (which is how long it can power a load with the engine off, such as your radio, laptop computer, headlights, etc.) to still pass a load test.
I had one such battery, an 85 amp-hour marine deep cycle battery (around 550CCAs, as I recall). I thought it wasn't quite lasting as long as it should so I charged it up and did a test. I used an inverter to power my desktop PC until it died. This particular battery, which had passed a conductance test with a Midtronics Incharge diagnostic charger (as well as a 100 amp load tester), only powered the desktop PC for 4 hours and 39 minutes.
Another identical (same make/model) marine deep-cycle battery, also passed a load test but powered the desktop PC for 10 hours and 25 minutes!
(I didn't sit there with a stopwatch, by the way. I just wrote a script to ping the desktop PC every minute from another PC and write the results to a file. When the pings stopped coming back is when the PC died due to the battery going dead).
Obviously the first battery was bad, but load AND conductance testing did not show any problems with it. I returned that battery and got another one under warranty.
The following links explain the problem:
http://www.batteryuniversity.com/parttwo-42A.htm
http://www.batteryuniversity.com/parttwo-42C.htm