Low 12v Batery

Is it the original battery? It’s 4~5 years old, fairly typical failure time. Do you have a digital multimeter? I’d start by checking its voltage (with the car off), and post here.

 

It’s not recommended to use a Prius car to jump start another vehicle, but the other direction isn’t a problem, if done carefully. See “If the 12-volt battery is discharged,” Owner’s Manual (PDF), pages 729–734, or Toyota’s official video. The usual way people get into trouble here is to connect positive (+) to negative (–) or vice versa; there are many PriusChat threads about damage done by reverse-polarity jump starts.

If you decide to replace the battery, the size is called LN 1, 140R, or H4, and it’s an ordinary “maintenance free,” flooded lead-acid battery, not an AGM battery like those in older Prius cars.

 

1) you can try that, if you can wait. it may or may not start.

2) you can try to jump start from another car, be careful not to cross pollinate the positive and negative connexions.

3) instead of paying for roadside assistance, spend it on a lithium rechargeable jump starter.

if the car starts in one of these scenarios, drive to an auto parts store that offers free load tests. if it passes, you'll need to charge it. hey may do it. if not, buy a charger, or drive it (or leave it sitting in ready) for 8 hours. it takes a long time for the car to fully charge the battery.

if you don't drive much, you will need to keep a battery maintainer on it to keep it from going flat.

if you can't get the car to start, you'll have to pull the 12v and take for a charge and load test

 

Your Owners Manual gives some good instructions on jump starting your car with another vehicle in section 7.2, under If The 12 Volt Battery Is Discharged (page 646 in the one for my 2022).
From the Warning Message I would assume the voltage is a bit low and would recover enough to start it when it gets warmer (not unusual for lead acid batteries).

 

Batteries do not "discharge" due to cold weather.

But old batteries will lose capacity over time and will "self discharge" when just sitting.
Low temps will further reduce the capacity WHILE COLD which will recover some when it warms.

Regardless of which immediate option you choose, your second move should be to get a new battery.
Your 3rd move should be to keep the battery charged with a tender type charger if you don't drive it very often.

 

Honestly, the Battery University (yes, it really exists) states that a 3 to 5 year lifespan is “normal”. Even renewable energy installations advise replacing lead acid batteries that have been “babied” every 5 years. Yes, they can last twice that or better, but 5 years is nothing to scoff at. Get it jumped, head over to your dealership and have them put a new one in (yes, you can get a cheaper one, but if it’s the Toyota recommended one and the dealership installs it, you have 2 full years where it is 100% Toyota’s headache, not yours).

 

That can be remedied. You don’t need expensive, and they have lots of uses.

for a more in-depth assessment, there are DIY electronic load testers. Many automotive retailers selling batteries have pro level testers and will assess the battery for free, good for business.

 

the warmer the climate, the shorter the lifespan