I've just done my annual battery testing and my process is similar.

I happened to automate the process and as such it works like this. I
have a small PLC that does the work. The battery is connected to a
resistive load to generate a roughly 0.6 Amp draw. The PLC looks at
the battery voltage once a minute until it reaches 10.5 volts ( I
chose 10.5 because I did want to stress the battery a little). The
PLC records the total number of minutes and once the 10.5 volt limit
is reached the load is disconnected and the battery is switched over
to a charger for a recharge. I can start a "test" at any time and
come back later and read the run time. With the battery going back on
charge automatically, I'm not worried about it sitting discharged at
the end of the test.

Now for the interesting part...

Back in march of 2008 I bought 2 new 7AH standard sized batteries and
tested them "new". They both went approximately 540 minutes. I
purchased them from an electronics supply store in town. In 2009 and
2010 I tested and the run times were very similar showing little
capacity loss.

My brother had heard from another club member that Academy here in
Houston actually sold better batteries and he bought one for his
glider. I loaned him my tester and his battery went 800 minutes.
This is a roughly 50% increase in duration so I went and bought one
initially, tested it and found mine also tested at 800 minutes and so
I bought a second and replaced both of my batteries. The second one
initially tested at 730 minutes, but with 3 cycles came up to 800
minutes as well. On a whim, I weighed the original 2008 batteries and
the new ones and found that the new ones weighed something like a 1/2
pound more, both of them.

Also in my testing this spring I ran my 17Ah battery on the tester and
replaced it after it demonstrated some unusual performance. On the
first test it ran only 300 minutes, but when I noticed it had run only
a short time I restarted the test without recharging it. It ran 500
more minutes and then quit again. I again started the test without
recharging and it went another 400 minutes. While I'm not sure why
that was happening, I am convinced that it's not a condition I want to
chance while flying so in this case I think the tester identified a
potentially suspect battery and $40 to replace it is cheap insurance.

I'll try to get the brand info for the batteries I bought at Academy
and re-post. Something like "wildgame" or similar... Cost $21.

Mark