Possible 12V battery issue

Hi guys,

I have been having an issue with my Prius the last few weeks and I think it may be related to the 12V battery. I need some advice on whether or not I would need to replace the battery.

Basically the issue is that when I start up my car (put foot on brake and press Start) it acts like I did not put my foot on the brake and starts in "ignition on" mode. The main issue is that it does not go into READY.
But If I do it again after 5 - 10 seconds (foot on the brake and press Start) it will switch into READY and all seems fine.

Of course my concern is that my battery is not charged enough and I don't want to end up stranded somewhere needing a jump.

Here's what I have tried so far:

Figuring it's the 12V battery, I went to my local AutoZone and asked them to test my battery. His tester showed it was at 12.3V and was a good battery but in need of charge.

A week passed until I had a harder time starting the car and I went to a Toyota dealership so they can look at it. I told the guy I was having battery issues so he had someone test the battery. His tester showed the same results.
He asked me if I leave my car unused for days at a time. I said I drive it every day.
He asked me if I'm only driving it a few miles a day. I said I drive 20 miles to work. He said that still wasn't enough to keep the battery charged.
So he suggested I get a battery charger from Sears. I said "Are there any left?"
Anyways, I found a battery charger on Amazon, used it to charge up the battery overnight and I'm still seeing the same issue.

From this post "Prius won't become "Ready" | PriusChat" replacing the battery was the advice on the forum as well as the OP's resolution. Could that be the case for me too considering the battery tests to be good and the car isn't 4 years old yet?

Thanks in advance,

Jon

 

I got this CTEK 93-56-864 MUS 4.3 Black 12V Battery Charger and 93-56-382 Black Comfort Indicator Eyelet Bundle
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Yes I do have a digital multimeter. I can use a little advice on how to use it to test the battery. Do I test it with the car on or off?

I have noticed when I initially press the brake pedal, before I press Start, it seems a little tougher than normal. And when I press it the second time it is easier to press.


A couple other observations:
There have been days when it's been 90 degrees or more during the day and when I am leaving work and try to start my car it can take more than those 2 presses of the start button. It seems I have to press the start button and let the car sit in "ignition on" for a few minutes before I can press Start again and have the car go to Ready.

On that first press of the Start button, I can see that not all of the systems are fully starting. For example, the Audio/NAV display that shows the Toyota logo on startup may or may not show that until the car is in Ready. Also the power windows will go down at 2/3 to 1/2 of their normal speed.

I am almost totally convinced that I need to replace my 12V battery. Would a test with the multimeter tell me whether or not I need to?
If I do need to replace it, is there a certain kind of battery I need or will any name brand car battery do?
I know I can replace it myself since I was able to remove the battery to charge it. What's a preferred battery store or should I just go back to AutoZone?

Thanks again,
Jon