Clearing immobilizer error after 12v battery problem

I have a 2012 Prius with 150K mi. One day last week the car failed to start. The dome lights were very dim, and it looked like one of them may have been left on. The 12v battery measured 8.2v. BTW, this is the original battery-- 12.5 years old!

I disconnected the negative terminal and put it on a trickle charger for several hours. It measured 13v and I reconnected the neg terminal. Pressed the power button and the display panel lit up with all kinds of flashing lights (all except READY), including the immobilizer light. I called AAA for a tow to the dealer.

The AAA guy ran his tests on the 12v battery and said that it looks fine. He then asked me if I had used the key fob to turn off the immobilizer error. I told him that I didn't see anything about that in the manual. He told me to get in and close the door, then use the key fob to lock and then unlock the doors. ( He still had his jump pack on the battery). This cleared up all of the errors and the car started right up. He suggested that I drive it for about an hour to charge up the 12v, and it has run fine ever since.

Is this key fob lock/unlock trick something that should be in the manual?