Do I need to replace the 12V?

sounds bad. is the car starting? is the battery original? if so, just replace it. personally, i like a volt meter on the jump point.

 

yes, but it's easier done under the hood, inside of the fuse box. there's a red cover you flip open to expose a copper terminal. it's easier to jumpstart, than crawling in back to open the hatch manually if the battery is dead.

 

Yeah, me too. Measure the at-rest voltage, at the jumpstart connection under the hood, and post. If it's for sure less than 12.0 volts, something needs to happen, charging and or replacement.

Jumpstart point, from Owner's Manual, page 543 (astounding how many pages they need, to say just the rudimentary instruction *):



That's the positive connection point. The manual describes a negative connection point way across the engine bay. It's ok, but a reach: any bare metal of body or engine is good. For multi meter and charger clamp connections, I use a small bolt that protrudes from the side of the engine, where I've flagged with an arrow in the above picture. When we bought the car the 12 volt was toast (from sitting around). I watched them jump it and they used that bolt.

* For a trip down memory lane, how Owner's Manuals used to be written:

'58 Volkwagen Beetle Owner's Manual | PriusChat

 

It's unseasonably cold for us, on the west coast. This time of year it's typically 2~8C above zero, frequent rain. But right now, my phone is saying -7C. Ground a little white with thin snow, been sunny, but supposedly a system coming overnight, going to get some significant snow they're saying.

We've got (17") Michelin Pilot HX mxm4, they seem to be a special run, have the GreenX badge. Aftermarket versions apparently do not. Right now have Michelin X-Ice 195/65R15 on though.

We watched Sing Street the other night.

Also, loved Line of Duty, I believe seasons 2 and 3 were shot in Ireland?

 

Due to the inaccuracy of the voltage readings I can't say for sure your battery is good or no good. I will say I've seen those readings even with a new battery. The voltage at the "boost point" can be off by about 0.5V or so due to the long cable to the rear of the car. With current flowing. With no current flowing it should be right on. So no lights on, car off. If it goes below 10.5V the car may not reach "ready". I have seen a Prius reach "ready" with a battery slightly below 10V, but I was amazed, and I wouldn't want to drive around with a battery that bad.
Do note that as soon as the car is in "ready" the voltage you see is the inverter charging circuit, not the battery. Engine running or not. There is no alternator charger on a Prius, it's built into the hybrid system and runs at very high voltage. The inverter converts it to 12V battery charging levels.

Oh, and it's not winter yet. Try -22C for the last week. It did "warm up" to -18C once during the week.

 

When our car sits more than a couple of days I put on a smart charger, then just leave it on. When it's done it's just trickle charging, maintaining.

 

i'd say 50 mpg u/k is about all you can expect with those tyres. car is operating properly, the rest would be hypermiling techniques.

 

Check in the morning instead.

I've been monitoring my battery and it shows 12.20V in the morning. So far so good. I will recharge the battery to top it off.

 

12.4

 

For other Canadians out there:

I purchased the OEM Yasua DS46B24R battery for 229.50 CAD ( thats still the price right now in 2021) from agmautobattery.com which is actually a branch of Saskbattery in Saskatchewan. Shipping within Canada is free and it came within a few days. Found that better than the dealer which charged about the same price but a fair amount for shipping.