Yes, I was the original owner. I live in Ohio, so neither too hot or cold. The battery was getting weaker at the end. Still a very good life. Far better than all of the fear that is out there about early battery failure.
There are fancy testers and procedures available to check each cell but in the end, they are going to fail at a certain time pretty much no matter WHAT you do to them......and it's kind of like a heart attack; no real way to predict when.
The Toyota specific ODBII application can read the individual cells but I think that will just make you paranoid (more?).
Given the reports on here and other forums, my guess is that you should have at least a couple of good years left.
Just drive it until the first sign of electrical "weirdness" and then take it in for a complete diagnosis.
NOTE: 8 years would be a REALLY long run for the 12 V battery. If it is original, I suggest getting a new one NOW.