No electric in COLD WEATHER ONLY

Certainly a battery's power is reduced in colder weather, but how cold are we talking here? Unless the temperatures are sub-zero, the reduction in capacity would not be significant. Your battery could be weak, but are you really saying you see no light at all coming from your headlights when you turn them on without the car in Ready mode? My best guess would be that you have a loose connection between your cables and the battery or between the negative cable and ground. Possibly the connection becomes slightly better in warmer weather with thermal expansion, although at best I would say your connection is probably unreliable in any kind of weather. The connections to the battery in the rear is where I would look first, and then put a multi-meter on your front jump points to see what voltage you get. It should be 12.5V or better.

 

If you have a really old 12v and you live in a warm coastal area like Fremont, CA., it makes sense that it's finally gonna go bad when you take it up into the mountains where it's much colder and you're lucky it works at all after it warms up a bit.

It's time for a new 12v battery. Let us know if you need help deciding on what kind to buy.

 

If the connections on your 12v battery are not tight, thermal expansion can be the trigger between conductivity and non-conductivity.

Inspect and tighten the connections at the 12v battery posts.

A fully charged AGM battery should be showing around 12.85 volts. Lead-acid would be closer to 12.6 when full. I think your version of the car has AGM but doublecheck.

 

"Normal", not quite.
"Common" yes absolutely.

You have a bad 12 V main power connection somewhere, maybe INSIDE the battery.
You need a voltmeter to do some testing while it is failing.

In the mean time, check the battery cables where they connect to the posts.

 

How old is the lead acid battery ? The average lifespan is 5 years, and it's like they have a $@#!!## built in timer.
If the battery is 4+ years old, replace it..

jp

 

The 12 volt battery well may be full of water too. Many a Prius has bad cabin leak. if the car lives outside drill a drip hole in the rubber plug in that battery well.
don’t remove the plug it may present a lovely hole for mice to get into the car mice love a G2.

lots of people on other car forums report mice chewing on wiring so becoming
A common issue.

 

you'd have to be a really skinny mouse to get through a 3/8" drain plug hole...

 

Hmmm . . . my daughter has made mention something similar to this since winter began. We also replaced her OE battery this past fall. Sucker was a 2007 battery.

The first time she mentioned it she called me to tell me her car wouldn't start. She said pushing the "Power" button started the engine but the dash remained turned off. She pressed the "Power" button a few more times and it was all normal. Then a week or so ago she said that sometimes her car won't start (not sure exactly what "won't start" means) when its cold. I'll have to check the battery connections once more.