Battery maintainer install directly to 12V battery

Thanks. 4 day old owner of my first ever hybrid, so bear with me. What happens if the 12V battery dies? I was sitting in the car listening to music in my driveway and the dash had a msg saying "battery low, turn off car"....I imagine this msg relates to the 12v battery, right? Did it discharge in transport and/or sitting on the lot? I know I was told to pick up the car the day after the dealer received it.

 

You are correct. When you get that message, you should be able to switch to READY mode, which will keep your 12V battery charged. There is always a certain amount of parasitic drain from some of the systems which remain active while the car sits idle. For example, the door lock system remains active to detect your key fob to unlock the doors.

My Gen 3 12V battery would drain after being parked for about 10 days, so I made sure to drive it once a week minimum, but later, I installed a battery maintainer to keep it charged.

My Gen 5 has highly variable parasitic drain; sometimes going flat in 2 hours, and other times holding a charge for several days. If you plug in the hybrid battery every night, you shouldn't have to worry, as I believe it maintains the 12V battery. I always carry a booster pack just in case, and I keep it in the front seat. I learned the hard way that the only way into the car when the battery is dead, is through the driver door with a key.

 

Just so I'm clear, the "hybrid battery" you mention above is the high voltage battery, right? With what/where do you plug that thing in? And yes, I've attached a pig tail connector to the 12V battery to the right side of the "trunk" to plug in a Battery Tender.

 

Ah, I think I see the problem, you have a Prime, mine is the run of the mill variety!

 

You can connect the battery maintainer to any live wire from the battery or to the battery itself. Just be aware that alligator clips can lose the connection over time, leaving your battery to drain.

I'm not familiar with the car you own, but I was referring to the plug-in kind. Sorry, I kinda forgot that all Priuses aren't plug-in.

 

Okay, first off, never sit in the car using power without the car being in Ready mode. Doing what you did is one of the quickest ways to kill your 12V battery. Just have the car in Ready and let it cycle the engine on and off when needed to keep the 12V batt topped up.

A modern car, especially a hybrid like the Prius, uses a lot of 12V power to run all the computers/electronics when the car's awake. And since the Prius doesn't need to use the 12V batt for starting the engine(the HV battery does that), Toyota uses a pretty small 12V battery. So when you put a big load on a small battery, you can kill it really quickly. And lead acid batteries don't like that at all. Every time you drain it down, you do permanent damage to it. You can get away with it a couple times, but eventually it's too damaged to do its job and needs to be replaced.

So if you're going to listen to music in your driveway, leave the car in Ready and just deal with the engine running every once in awhile. As for what to do if you do drain the 12V battery flat, it can be easy or hard. Which way depends on if you have a jump pack in the car. A decent one is maybe $50-$75 on sale, and I highly recommend it.

If you've got one and the car is completely dead(the doors won't even unlock), then you use the physical key inside your keyfob to open the driver's door. Then pop the hood and grab your jump pack. Inside the engine fuse box(driver's side) is a small, red plastic cover. Flip it up to reveal a place to connect the positive(red) clamp from the jump pack. Clamp the black side to a metal part of the engine or body. Then turn it on and try to start the car. If the car still won't start(and the jump pack had a charge), go back to the rear hatch and open it. Then go back to the engine and grab the jump pack. Uncover the 12V battery in the cargo area and connect the jump pack to it directly. Turn the jump pack back on and try starting the car again. Now it should work. Either leave the car in Ready mode for an hour or so to get at least some charge into the battery, drive the car around for awhile, or remove the battery and put it on a charger. The best way is the charger, but the other ways work if you don't own one. (BTW, using the car to recharge a dead 12V battery is a good way to kill your alternator in a non-hybrid. But hybrids use a big DC/DC converter to pass power around instead of using an alternator, so I don't think it's as bad an idea to use the car to charge the 12V in a hybrid vs. a non-hybrid. But take that with a grain of salt as I'm no expert.)

If you don't have a jump pack and the car is completely dead, you are about to have a bad day(and just pray it's not at night). You open the driver's door just like before. Then you reach around and open the rear passenger door. Now you need to grab a screwdriver(philips I think), lower the rear seat back and crawl into the cargo compartment. Hopefully you don't have a bunch of junk back there or you'll have to remove all that first. Once you've crawled in and gotten to the inside of the rear hatch door, look around on it for a small panel held in by a screw or two. Remove the screw(s) and pop the panel. Inside is a lever to manually open the rear hatch. Pop the hatch and stick something into the gap so it doesn't re-close on you. Then crawl out, fully open the rear hatch, and remove the 12V battery so it can be recharged. Or just call a tow company so they can jump the car and you don't have to go crawling in the rear. (All this is described in your owners manual with illustrations, btw.)



So just to reiterate, the low battery message you saw was completely your doing and not because of anything due to the transporting of the car. At least you were inside the car and saw the message before the battery depleted enough to prevent it from starting again. So you've learned a valuable lesson about your new car without anything bad happening. Don't do it again, chalk it up as a win, and keep enjoying your car.

 

Excellent info. Thank you. When you say "start the car", that means getting all the electronics lined up to take off in EV mode, right, and not actually crank over the ICE like a non hybrid.

 

It means READY mode. Press the power button while pressing the brake. Just like when you do when you want to drive somewhere.

Whether the ICE starts or not depends on other factors. 12V battery voltage, HV battery voltage, ambient temp, climate control settings, and probably one or two other things I can't remember off the top of my head.

There are four power settings:
1. OFF
2. ACCESSORY
3. POWER ON
4. READY

You can cycle between 1 through 3 by pressing the power button without pressing the brake pedal. In order to get to 4, you have to press the power button while also pressing the brake.

It's best practice to only use OFF and READY. Avoid the other two modes. There are times to use them, but those are special cases. For example, one time to use POWER ON is when the car's computers need to be on but you can't run the engine. Like if the car is at the dealership getting a programming update. And the instructions for that include putting a charger on the car so the 12V battery doesn't deplete during the process. As an owner, only use ACC and POWER ON if you absolutely can't have the ICE start up, and then only for the shortest time possible.

 

Thank you sir! Still plowing thru the owners manual, so appreciate the patience and detail you have provided.

 

Also, does the car have a conventional starter motor, or is it the HV electric drive motor handling the ICE starting duties?

 

I attached the CTEK quick-connect positive (red) ringlet where the 12 volt feeds into the fuse box, under the black-plastic cap.

Removal of that cap is shown in a @NutzAboutBolts video, video #23 here:

Nutz About Bolts Prius Maintenance Videos | PriusChat

you can also see the neg (black w/ red stripe) connection here. It was an unused, threaded hole. An extra bolt is needed, believe M6:

 

Thank you

 

The cap removal video makes it look easy, takes him a minute. Even after watching the video it took me at least 10~15 minutes. These are the two tab locations; you need to lift up on the cap while gently prying the release tabs at the two flagged locations, back-and-forth.

 

I never use the ACC mode. There's no reason for it in my opinion. My first few weeks owning a Gen 3, I was testing things in ACC mode, and the 12V battery went dead in less than 15 minutes. The battery turned out to be faulty, and was replaced. It could have adequately started the car for years more, in that weakened condition.

But a poor 12V battery should be adequate for much longer than it would in a conventional car, due to the fact that it has no starter to crank. All it has to do is start the system, and the DC-DC converter takes it from there, providing power to the 12V system.

 

When I connect the Noco Genius on my Gen 4 Prius Prime, I pass the AC cable on its flat side on the headlight groove and then completely close the hood so that if someone gets to the car in the garage, they cannot tamper under the hood.

 

I’m doing something similar with our gen 3, just for the block heater cord.

 

I do the same, but I make sure not to allow the cord to flop in the wind by keeping the exposed part as short as possible. The wires inside the cord will break because of this.

 

Couple more thoughts:

Considering sooner or later you’ll forget to unplug, make any through the grill electrical connectors short and VERY securely tied. Also make the external connector easy release.

For an external charger and internal quick-connect wire, I would not run that out through grill: the quick-connect is basically a route to the pos and neg battery posts, and some joker with a paper clip could ruin your day. FWIW the CTEK quick-connect is fused, but still… For an on-board style charger, cord through grill is ok, it’s just AC connection.

 

Good point. I only did that once. Dragged the extension cord all down the driveway.
Use a cord with a connector that isn't too tight, so it will let go.

 

I've dragged one for 10's of kms, the prongs were bevelled off from abrasian.