12V Battery Drain Issue

I wonder whether your battery is no good in the first place. I just replaced mine today registering 12.6 V with no load. The old one was down to 11.8 V, and when I plugged in a scangauge, the car threw a hissy fit and the dashboard lights cam on including the triangle of death (or so it seemed)

 

Extremely common problem.

Don't bother getting the battery diagnosed because its a very small battery and when you kill it good just once it sulphates much quicker than a large battery.
Remember the first time it went dead? It was toast then.
Sulphation is a chemical process that happens to the charging plates when the acid looses its charge.

And it kills the battery for good. Once its sulphated it will never hold a full charge again so it cannot deal with the standby current draw on a Prius although not large is much larger than most cars with a big battery.

Yuor putting it on a charger and its taking a charge just enough to start the car but it will not store that charge for long and if you notice the current draw meter on the charger never gets close to 0 current draw.

When you get the new battery once a month throw the charger on the car using the front jump terminals. In 2 amp mode in 5 minutes it will charge the battery to max. Its very very good for the battery as the car cannot put a full 100% charge on the battery and more importantly it will tell you real quick how healthy the battery is by how long it takes to complete a full charge. A full charge is when the current meter goes to 0. Alot of us do that routinely with our Prius's.
A healthy battery will charge to full real quick. A sick battery like the one you have will never complete a charge no matter how long it stays on the charger. It will always show current draw no matter how long the charger is on it.

I'm going on 5+ years on the stock Prius battery with no issues. In the last 25 years I can't remember ever having to buy a new battery on any car I have owned.

 

when leaving a car for an extended period of time, such as while on vacation, it is recommended to use a battery disconnect which prevents the slow drain of the battery from alarms and immobilizers, and the SKS system is probably using juice 'looking' for your fob awaiting your return. As an added bonus, when parking your car for extended periods you unscrew the green thing which disconnects your battery which also makes your car much more difficult, annoying and time consuming to steal.

Unfortunately in a Prius there's a whole bunch of crap on the positive terminal, so I would recommend having a professional install a terminal disconnect, which the one I'm showing was less than $4. And every time you wanted to disconnect and connect the battery you would have to go into the trunk and remove several floor panels. It would be annoying but if you go on long vacations it would be worth it because you would prevent batteries that are not that old from going bad.

 

Isn't the prius battery terminal an odd size, so that disconnect may not fit?

 

Do not use a boost charger on the Prius OEM battery it is only designed to take a maximum charge rate of 4amps.

 

If you re-read my post you will note that I did recommend having a professional install the terminal disconnect. And it is probably adjustable to fit all sorts of post sizes.

I know a lot about tires but very little about automobile electronic systems, does anyone know if a battery disconnect could be attached to the negative terminal and would prevent the battery from draining if not driven the car for weeks or months?? I think I recall a lot of DIY maintenance threads on here ask you to disconnect only the negative lead to the battery.

I didn't read the back of the package so I have no idea if it has to be attached to the positive terminal or either one.

 

Sure you can put the disconnect on the negative side.


As to your other question you should always disconnect the neg side first because if you don't and your wrenching on the pos terminal first and you hit a ground by mistake with your metal wrench it can ruin your day, where of course if you hit a ground and the neg is already disconnected your fine.

 

Well there you have it, anyone who is going to go more than 10 days w/o driving a Prius should have a terminal disconnect installed on the negative terminal. You can take the green thing with you or just hide it somewhere in the car.

Either way you will then have to separate the mechanical door key from the remote in order to get back into the car. Then you simply screw the green thing back onto the disconnect and you should have a battery that has almost the same amount of juice in it as when you left the car weeks or months ago.

In addition, if its going to be in your garage while you're on vacation you should also jack up as many axles as possible to prevent the tires from warping. If you only have 2 jacks stands, do the fronts as it puts more weight on the tires, if you have 4 jack stands jack up all 4 corners. If nobody will be entering the garage and there is no chance of someone bumping into them, you can jack up the front on jack stands, jack up one of the rear corners with your pump jack, and the other rear corner with the factory scissor jack.

 

Or go here for another solution..

 

If you have a terminal disconnect in the negative lead you will have to crawl into the boot and remove all the floor panels every time you get back in the car.

 

i never said it would be easy, that's just the punishment for abusing your prius by not driving it on a daily basis.

if I recall you install the small floor piece that covers the battery area before installing the rest of the floor. If instead you install this piece last, it may not lock into place properly and you will be able to easily remove and replace (not fully seated of course) the small floor piece, thus allowing you easy access to the battery compartment.

some might argue this might result in battery fumes leaking into the passenger compartment.

 

Yes the battery minder is great and I have one too but using the basic charger with amp meter on it cannot be beat for battery diagnosis. If it refuses to take a complete charge or takes forever to reach full charge that will give you all the warning you need.
Thank you.

 

Yes a battery disconnect is very impractical for sure in the airport scenario but very practical if you need to disconnect it for a few weeks in the garage. Just put the hatch down but don't close so you can open it again.

I would not like to climb over the seats and open the hatch from the inside.

 

A note: the VDC Electronics Battery Minder I use does not change to maintenance mode (green LED flashing) until full charge condition exists.
(see here)

 

I connected a battery disconnect switch a few years ago and have used it several times to my advantage. I installed it in series with the neg lead on the side carpeting. There is a small plastic plate for tail light access, and it fit perfect there. This Summer, left the car for three months with no problem. It also came in handy for rebooting. :cheer2:

 

Not to be greedy or anything, but could you possibly post a pic of the intallation? I am thinking about doing that as we leave ours in parking lots for 2-weeks to a month and cannot feasibly use a battery tender/float charger. Our 2012'hatchback should be similar to your PIP.

 

In March 2020 Toyota UK sent an email about Covid lockdown and Prius inactivity and how to keep the battery charged during little or no use.
What they say is enter the car, start the car using the start procedure as normal, you will get the green `Ready' lamp showing. make sure the heater and a/c is switched off and anything else, radio, lights, whatever.
You should leave the car in the 'Ready' state, leave it for an hour or more. In this 'Ready' State the Hybrid battery now runs things and also sends a charge to the 12v battery.
Occasionally, the engine may start/stop, so that the Hybrid battery itself gets a charge to maintain the correct hybrid battery voltage.
You can leave the car like this for hours if the car is not needed. Its a good idea to get a cheap key cut especially for this procedure so that you can manually lock the car for security purposes.
Once the car settles and 12v battery gets charged the engine will start/stop less frequently.
So remember:
The Engine charges the Hybrid Battery,
The Hybrid battery charges the 12v Battery.
The 12v battery does not need the engine constantly running to charge, which is obvious, but just in case of misunderstanding.

Toyota said this will keep your car battery from going flat in periods of low or no activity.

You might want to add JMP Battery Monitor II (a Bluetooth device with a smartfone App that can tell you the battery voltage without touching the car). It Fits across the battery + & - terminals. (no it won't drain the battery itself!)
IMHO and experience this will see you well when you have to cope with Prius 2 12v problems.
PS use a timer on your phone to remind you to turn off your car, since it can sit quietly and we can forget it's on.
Hope this helps.

 

in the email dis they say how often one needs to do this? Weekly?