2015 Toyota Highlander Hybrid 12v battery replacement - Hybrid won't start

Replacing the nine year old 12v battery in a highland hybrid. Lately, and once every two weeks, the vehicle hybrid system won't start. Some interior lights come on, but the electronics are in a funky mode. I had the battery tested twice and the shops said it was good. But the battery volts kept draining. Replaced easily, and car runs smoothly, and starts quicker.
note: Yes I know to remove the black negative line first. I got crowded with the yute and the recording device.
Update: At 100 miles on the new battery, I have 30.1 MPG. That MPG is similar to when I drove the car off the lot. I have averaged 28.7 to 28.9 for years.