I was waiting in the mall parking lot while my wife got her hair cut. I never got out of the car, so the headlights stayed on and drained the 12v battery. A good Samaritan "jumped" the car with a portable jump-start device. The next morning, I hit PriusChat and found out about the system diagnostic. It shows that battery has one foot in the grave and another on a banana peel - 12.1v at rest and dropping to 9.8v with the dome light on for a few minutes! Back to PriusChat to research replacement batteries, their sourcing and installation. I have an Optima Yellow Top on order, as well as a pair of those jump-starters (One for the Pruis and one for the pickup). Before I install the new battery, should I have it trickle-charged overnight? Thank you all for this great forum. It's saved me hundreds of dollars on my old 2006 and my "new" 2008.
Cows are outa the barn so not much point to closing the doors now, but: If that was your first accidental draining, a charging session might have brought your existing battery back up. Look for a "smart" charger in the 3~4 amp range. A digital multimeter is another handy tool to have, not just for checking the battery, lots of uses. Anyway, yeah: it's a good idea to hook the new battery up to a charger, let it fully charge before install.
Obviously your wife needs to keep her hair long. And you have to go into the mall, and hang around the food court eating bad food and drinking smoothies, and agree to meet at Sears later. That'll solve your battery problem.
I ordered my 12volt from Elearnaid. It sat in the garage for about 40 days before I installed, I called them to be sure it would be ok, and it was. Also this video on ebay is very helpful for the install. Very easy to do
Actually, this was the third time I had difficulty starting the car after sitting in it. I only just lately recognized the starting issues for what they were..I drove the car about 60 miles, then let it sit overnight before trying the onboard diagnostic. The battery is toast. I may, however, retask it for use in a small solar setup for my shed lighting.