Small red Triangle About the park button?

This is a hallmark of a depleted/weak 12V (accessory battery).

The battery itself will run you ~$150, plus install (unless you DIY, which isn't that hard). There are replacements (such as the Optima) that some claim is better than the OEM for not much more.

 

Yep, what pjc said.

Since the Prius 12V battery doesn't have to crank the engine (the main traction battery does that) then you don't get that early warning of slow cranking like in a conventional car. So usually the first thing people notice is some weird behavior of the electronics exactly like you're seeing now.

Yes, the battery you need to change is the little one behind the right wheel arch at the rear of the hatch.

 

There's probably a guide here somewhere but sorry I don't have one bookmarked so you'd have to search. It's not too difficult but a little more fiddly than a regular car. There's a small rubber vent tube that you have to attach (very easy just pull off the old battery and pop into the new) and small section of ducting and a capacitor box that you have to remove to get access.

Tip. Remove the negative first at the body end of the short ground strap and leave it connected at the actual battery terminal until it's removed from the car. Assembly is the reverse.

BTW. Make 100% sure you have new battery inserted the right way and polarity correct before connecting anything. You can't get it wrong even for one second without potentially doing a lot of damage. So there must be no trial and error involved!

 

You can replace the battery yourself. The choices are if you wish to keep things simple:-
OEM battery from dealer.
Optima.
Exide edge battery FP-AGM51JIS.

Sorry do not know part number for the Optima. All are direct fit The OEM and the Exide have the longer guarantee and the Exide has the highest capacity.

John (Britprius)

 

When you look at the negative battery cable you will see that one end is attached to the battery terminal while the other end is bolted to the body.

It is much easier to remove the bolt at the body, than to try to unbolt the terminal connector while the battery is in the car.

If you still have trouble with the concept, just remove the trim panel to gain access to the 12V battery and you will see for yourself.

Here is info about the Exide battery:
Another battery for the Prius. | PriusChat

 

The battery negative on most cars just connects to the chassis (ground). This short thick wire is called a ground strap. All I'm saying is that's it's easier to remove the battery from the car complete with ground strap attached than it is to try and disconnect the negative battery terminal in the confined space back there. Hope that makes sense.

Also when reassembling it's easier to attach the ground strap to the battery negative before you place it in the car. An added bonus of this is that you then can't really go wrong with the polarity, assuming that is that you've correctly attached the strap to the negative terminal first up.

 

There is no resetting the computer. The only things that will need resetting is the drivers window auto close (open the window half way close and hold the switch closed for about 3 seconds) and the radio presets. They are fleecing you on the Price of the battery and on the fitting. Walk away, no run.

John (Britprius)

 

The Exide and the Optima are around $150 the OEM battery is around $100 from reports here on PC.

John (Britprius)

 

If you get the Optima make sure it has the JIS terminals (Japanese Industrial Standard) these are small terminals fitted on the Prius Look up Erlinaid for the Optima. There is a new range of Toyota OEM batteries that have a longer guarantee and the price has come down. Your dealer is trying to sell you old stock at the old price or worse new stock at the old price. He is also trying to frighten you with talk about resetting computers.

John (Britprius)

 

Because the major auto parts retailers keep the "retail" price high and then discount it with coupons/promotions. Most of the time you're able to get one for $40 to $50 less than the list price, especially if you purchase at their web site and pick it up at the store or have it shipped for free to your home.

 

The Prices I am quoting are those reported on PC. Prices in the UK apart from the Optima are much lower. The Optima in the UK is well over the equivalent of $300. I believe the Exide is the better battery, but I know there will be people that disagree.

John (Britprius)