Prius Startup problem - not getting to 'Ready' after 12v replacement

Hi all -
A few weeks ago my Prius would not start at all, the dash lights would flicker in very weird ways, due to the 12v battery beginning to fail (I measured it at less than 10v), so I bought a Optima Yellowtop battery and installed it, which at first appeared to fix the issue.

Ever since then, I've had try multiple times to get the car started. I will get in the car, press the brake down, and hit the power button, and everything seems to come up properly except for the 'ready' light. I'll then turn off the car and try again, sometimes this goes on for 5-10 attempts, but at least so far I have always been able to get the car started. The worst times are in the morning and when I'm leaving work when the car has been sitting several hours, I pretty much always have to try multiple times. If the car has only been off a short time it starts up with less attempts, usually on the first try.

These feel like weak battery symptoms, but that would be surprising given I just installed a brand new one. I've used my multimeter to measure the battery voltage as it was sitting in the car and it was over 12v). I've looked at the terminal connections and the ground connection to the car and they all seem to be tight. I've been driving the car at least 60 minutes a day for the past two weeks after the battery was installed, that seems like even if the battery initially had a low charge that should be enough to recharge it.

Has anyone else experienced this?

 

Thanks - I should have mentioned I tried that as well, I own one of these -

One morning I tried charging the battery, the charger initially indicated it was charging the battery but only took about 2-3 hours to get to the 'full battery' indication, which seemed like a pretty short time if the problem really was a discharged battery. The car did start up after this on the first attempt but then the next day it was back to needing multiple startup attempts.

 

I installed the battery myself - I forgot to clean the terminals before installing, I will try that today - however the terminals looked very clean before installing. The connections to the terminals are very tight and the connection from the negative to the body also seemed very tight but I will check that again as well.

 

Would I see any other symptoms of the brake switch being bad? I've seen this mentioned before as a possible starting problem but it appears that my brake lights are still functioning properly when I hit the pedal.