12V and Electrical Issue

Yes your mechanic seems to have no idea

If you have a warranty on the new 12v battery, you might want to have that battery checked. A good battery should be over 12.6v in a Prius.

 

The new battery can be a bad battery? One that has sat around way too long before you got it? Just because it's new, does not mean it is good.

You can fully charge it and then have it tested. If it tests good, then you can start looking at your car as the problem.

 

There are many threads here regarding battery issues and many times, a new battery will solve the problem.

I'm not exactly sure how old was your "old" battery that you tested "good". But there aren't that many things that can cause your car to drain the battery.

1. Do you have anything after market installed?
2. Do you have any warning lights on the dash? Telling you the DC/DC converter is not charging your battery?

 

Would appear the 12v is low (like JC91006 said above).

If you have the SKS key fob (keyless entry), there is a switch underneath the steering wheel you need to turn off when not using the vehicle for an extended period (else it will drain the 12v battery). Make sure your physical key works in the door lock before turning off your SKS feature.

If your mechanic doesn't have a proper 'AGM compatible' 12v battery charger, you can let the car charge the battery (it does so slowly while driving or in "ready mode"). Once you have the car in 'Ready' mode, let it recharge the 12v battery by leaving it turned on for 8 to 12 hours (just sitting in park with the emergency parking brake engaged is fine). Make sure you have gas in the tank, as the engine with cycle on and off over that period of time.

If the 'new' battery refuses to hold a charge, then you should take it back for a refund or replacement.

 

Which battery is installed in the vehicle? Old or New replacement? You never returned the old battery for the core charge, when you picked-up the new replacement?

1) You don't know how the Prius works. The 12V battery is the most likely culprit.
2) It is possible the new replacement battery was defective or not fully charged before installation.
3) Does you car have SKS? Disable it, if the car will be sitting for long periods of time; read the owners manual for How To.
4) What battery did you purchase as the replacement?

It should be a 45AmpHr, AGM (Absorbed Glass Mat) battery, available from your local dealership and auto parts stores.
If you purchased an Optima, you made a bad purchase. The Optima is a 38AmpHr battery. Prius w/ SKS came equipped w/ a 45AmpHr battery. The Opitma has 7AmpHr less capacity, which translates into less stand-by time.​

5) Many shops and auto parts stores test 12V batteries w/ a Load Tester, that measures CCA (Cold Cranking Amps). This test is worthless for the Prius 12V AGM battery, as it does NOT Crank the engine, like a traditional car. FYI, the Prius High Voltage battery cranks the engine. Many times, load testers return a false positive that the Prius battery is good. The Prius 12V battery is used to power up the various ECUs (think computers) in the car; these computers tell other computers and various mechanical devices what to do.
6) JC pointed out another culprit draining the 12V battery: aftermarket accessories/modifications.

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Is my inverter coolant pump slowly failing? | PriusChat

Read post #5- How to apply a load to read the 12V battery SOC (State of Charge)
Read post #8- Smart AGM compatible battery chargers.​

A 12V that is in a regular state of discharge, like your battery, will live a shortened life, as yours do. Get a smart AGM charger and maybe just recharge the battery every other week. The CTEK or Noco would be perfect, as these two chargers include a "pig tail" that you can leave permanently attached at the battery terminals.

 

Far from being an expert, but your description cries "Bad 12v battery."

there have been lots of threads on this forum where an auto shop has tested a 12v and declared it good, yet it does not work in the Prius. There is something about it I don't understand, but plenty of the folks here do and maybe one of those will explain it for you.

I am reluctant to suggest, but, if YOU TAKE ALL THE PRECAUTIONS __ RTFM __ (that is read the FXX manual), you might try a jump start of the Prius and see if starts. That would tell a lot. The problem is you have to make sure you do it properly. I take no responsibility if you do not.

The battery may have been fine when you installed it, but there may be something that is wrong that is slowly draining the charge from the 12v. As said before, the mechanic advice you got....well....

 

WOW! A mechanic told you that?! It doesn't sound right to you because it's nonsense.

As stated before, either the new battery is low due to sitting on the shelf too long, or some accessory is draining your 12V battery.

 

Just to reiterate, the 12 V battery may not be the problem, but at 3 V, it is a problem and one you need to rectify before doing anything else. It will be impossible to diagnose the car with the 12 V in this state. It may be too late to recover this battery, depending how long it has sat in this severely discharged state. Once you have good and reliable 12 V supply, you can then determine if that is the only problem, or whether there is some other problem causing a unusual draw on the 12 V system while the car sits idle.

This is certainly part of the problem. For all the time the car sits idle waiting to be sold, you need to have the 12 V battery on a fully automatic multistage charger that has a maintenance function and an AGM setting. Period. No argument.

 

put a battery maintainer on it while it is sitting.

 

If your battery was 3 V, then 2 hours is nowhere enough time to fully charge it in car. Try 16-20 hours. Test your battery voltage again two hours after shutting off, that will give you a better idea. The 14 V is just the surface charge.

Yes, either of those brand are good. Look for one that has a max amperage of 4 Amps.

 

When the care is READY, 13+-14v is normal, and is expected to be seen; how else would the 12V battery get charged?

You installed the new battery, that was allowed to sit unused, for at least 6months, and in this time period the battery will discharge normally; the extent of discharge is unknown as you did not measure its SOC before installation. It does not help that you had this new battery installed w/o being fully recharged either.

I will double down that you have a 12V issue.

1) You installed an Optima that was in a discharged state.
2) You don't drive enough.
3) Assuming you have SKS, the Optima is severly taxed/overworked, b/c it is in a perpetual discharged state.
4) The Optima is either now damaged and NO LONGER reliable, or it may possibly have some life left if you recharge it.
5) Invest in one of the three smart AGM chargers I listed, or do your own research and buy your preferred smart AGM charger.
6) Recharge this depleted Optima w/ a smart AGM charger.
7) For the love of God, read post #5 & #8 in this link:
Is my inverter coolant pump slowly failing? | PriusChat

Read post #5- How to apply a load to read the 12V battery SOC (State of Charge)
Read post #8- Smart AGM compatible battery chargers.​

8) Once this Optima is recharged, See what the SOC is the next day, by applying a load as listed in post #5 from the thread, Is my inverter coolant pump slowly failing? | PriusChat
9) Buy a Digital Volt Meter (DVM), as you most likely don't have one. This is very useful tool, just like a screwdriver, hammer, wrench, socket set, tape measure.​

 

low 12v could cause that.

 

You realize you make no mention of this until Post #17.