Key fob randomly dead, car is dead but interior lights dimly blink

Initially, just charge the existing 12V battery. Or even begin with a jumpstart (caution is necessary, as user error here can be very expensive.)

After that, 12V battery replacement may, or may not, be needed, that remains TBD.

 

Why not use a digital multimeter (or "digital volt-ohm meter") to TEST what the voltage is at the battery and at the jump start point under the hood?

A weak 12V is very likely- esp since I haven't heard anything good about yellow top batteries. But you should confirm what's going on before proceeding.

Posted via the PriusChat mobile app.

 

Yep... YellowTops are the worst 12v batteries. They were industry leaders decades ago, then they got bought out and new owner has zero quality control standards. The reason they're commonly used in Prius is that only thing a 12v does in a Prius is turn the computers on and flip some relays that turns the hybrid battery on then that's it. After that the car's hybrid system sends a 14v charge to the battery till the car is turned off.

So Prius owners only use their 12v battery for a second or two each time they start the car, which makes for an easy target to sell a garbage battery to... Here's the one I recommend. It's 55amp-hour, which is 15amp-hours more than the ones they sell for Prius at auto parts stores.

I've had a 12v like this in my Prius for 10 years without issue: https://ebay.us/vN4JsP Also pics below are the hardware you need to mount your terminals to this battery.

 

That looks like the engine immobilizer light, which should be flashing whenever the car is shut down normally. It doesn't indicate any problem, and is not the cause of your dead battery (at least in the space of a few days or weeks).

Think of it as a cheap alarm indicator, following in the footsteps of fancier car alarms that have flashing indicator lights meant to scare away thieves. Lots of cars have this built in now, even if it indicates no more security than a simple fob-based electronic key system.

 

When you put the key fob in the slot it does something that doesn't use the battery in the fob. The security light stops flashing so the car recognizes the key. Now you need to measure voltage to see what's going on. If the headlights don't work then the voltage is really low or possibly you hooked the charger backwards and popped some uses?

Posted via the PriusChat mobile app.

 

If your battery is dead enough......or BAD enough......simply connecting a charger is NOT enough to make everything functional immediately. Even with a fairly high capacity charger, at least a half hour likely will be required.

You also could have a loose main battery connection.

 

Keep an eye on it, in case it is seriously wounded. It takes very many hours of driving (or sitting in Ready) to full charge a Prius 12V battery. Many ordinary driving patterns are not sufficient to keep it fully charged, so an occasional topping up with a battery tender may help, and extend its life.

 

^^This. +1

 

700 miles in a single day, will get it fully charged.

Spread over a full week, with many stops? Probably not completely full, but it will be fairly close, considerably better than the average Prius owner.

 

No reason to guess.
The battery and the charging voltage can easily be tested.