12V dies every two years

Not saying it’s your situation, but letting the 12 V deplete excessively even a few times can destroy it.

 

Are you sitting in your car with lights on after you turn the hybrid system off or something? Do you keep the charger plugged in, which reportedly drains the 12-V battery? No, this is not normal. You are probably doing something wrong. It should last for many years under normal conditions.

 

you're going to have to measure the current draw with the car off, to see if it is excessive.

sitting during covid might be the only problem, and don't leave the car plugged in, that will drain it.

 

My 2017 has the original battery. I don't give it any special attention. If I get home at 2 or 3 PM, I plug the car in and usually unplug it the next morning. I expect it to someday fail, so I carry a small 12V jump starter in case that should happen when I am not at home.

 

There was/is a problem in some Prius Primes where the Safety Connect communication device does not turn off as it should when you turn off the car. As such the Safety Connect communication device is always drawing 12v power. Solution has been software fix by dealer.

 

You should be able to get at least 5 years out of a battery unless you deplete it a few times where it won't start the car.

 

I always check the electrolyte levels in all my car batteries in the fall and usually get 8 to 10 years out of them. Two year battery replacement on a daily runner; you've got an internal drain somewhere. As Marine Ray stated; something isn't turning-off. The problem here is also complicated by the CPUs in this car that will only charge the 12VDC battery to a point, then redirect the current to recharge/regenerate the traction batteries. On a conventional car, as long as the engine is running, the battery is being charged.

Making sure you car has all of it's software updates would be a good start.

Hope this helps.

 

my 2020 is still fine, though my mazda3 i only got 3 years out of, upgraded that to a Northstar and never saw a lick of problems again.

 

You should easily be able to measure the current draining from your 12-V battery using your smartphone.

Your smartphone has a Hall-effect sensor, which measures the magnetic field B. You can install one of many apps to measure the magnetic field B. The magnetic field B is directly proportional to the current I through the battery wire and inversely proportional to the distance r from the battery wire. Note that you need to align the sensor to get the maximum magnetic field, which is in the direction perpendicular to the wire.

The current I is given as:

I = 2πrB ∕ μ₀

μ₀ = 4 × 10⁻⁷

This simplifies as:

I = 5rB × 10⁶ (I in amperes, r in meters, B in teslas)

or

I = 5rB (I in amperes, r in centimeters, B in gausses)

Therefore, if you use the gauss scale in your smartphone and use centimeters for measuring the distance from the wire, all you have to do is to multiply the distance r with the magnetic field B and then by 5 to get the current I in amperes. Make sure that you orient your smartphone to get the maximum magnetic field, which is perpendicular to the wire. However, you need to measure the magnetic field away from the wire with the phone oriented in the same direction as when it was close to the wire to account for and substract Earth's magnetic field, which will also be significant.

 

A more easy way is to use a multimeter with an amp scale. I have a Fluke 77 multimeter. First move the common (black) lead on the multimeter to the 10A input. Under the hood, remove the negative (black) battery lead. Ensure that everything is off on the car, the doors are closed, and the key is not in the ignition. Touch one lead of the multimeter to the disconnected negative battery lead and the other to the negative battery terminal. You have now placed your multimeter in series with any power drain on the car. Read the output. With no drain it should read about 50 milliamps. Much more than that, you have a parasitic drain. To find it, start pulling and replacing the fuses, one by one until the meter reading drops. Start with the fuses under the hood. If there are fuses under the dash, you will need to disconnect the meter, open the door, then put a clamp on the door light switch to ensure it stays off while you are in the car. Then reconnect the meter. Eventually you will find the circuit that is causing the current draw.
I understand what Gokhan is saying as I am a former Master Chief Electronics Technician from my Navy days. But you need to measure the amount of current draw, not just note that there is one.

 

That's not really the easier way. That's because you need to disconnect the 12-V battery, which will reset everything and then you will have to reprogram it. Not to mention the need for tool use. I wouldn't suggest the Hall-effect sensor otherwise. A multimeter would be useful if you want to determine the exact current during a certain situation. So, perhaps you can do the diagnosis you mentioned with a multimeter but at the cost of disconnecting the 12-V battery.

There is probably a third way though, which would be the best way if you could figure it out. The 12-V battery has a battery sensor installed on the negative (−) terminal. If you can access the battery-sensor information using an OBD-II reader, it will display the current, voltage, battery temperature, SOC (battery charging percentage), SOH (battery degradation percentage), SOF (starting performance), and self-diagnosis result for the 12-V battery.

 

Excessive parasitic draw is sure to be the issue. Normally these cars will be 10-30 ma after a short shutdown period of 5-15 minutes. Finding the sorce of the excessive parasitic draw is typically the hard part.

Using a dc clamp meter to read 50 ma or lower is not reliable in the least. That applies x10 to some attempt to use a smart phone's sensor. A direct series connection is the preferred method and can be done without losing settings. One way is to put a jump box on the cables prior to disconnecting them to insert the meter. The more common way most mechanics use simply uses a procedure that includes a jumper as illustrated below.

 

You guys also must remember the delay power-down sequence and sleep timers. Bring your fob within range, certain things power-up and your back to square one. Open a door, the current draw will jump. Asking your phone for a status update on your car will do the same.

You'll have the least amount of variations by placing a meter in series.

Hope this helps...

 

Minimizing parasitic draw by customizing the various settings such as setting the interior lights not to come on every time you approach the vehicle with the fob, the interior light delay to the lowest setting, coming home light delay to lowest, etc. etc. can make a huge difference in battery life and even help MPG usage. Even little things like remembering to close the windows before shutting it down (so the hybrid system powers them instead of the 12 volt battery) can make a lot of difference. We even go so far as to put the fob to sleep once we get home so it isn’t communicating with the Prius all the time.

 

Yes, I figured this out after I posted and I was going to post about it. Using a shunt wire before disconnecting the negative terminal to connect the ammeter in series would solve the problem of disconnecting the 12-V power from the system. However, one needs to be careful with the connections and remember to connect the shunt wire back before removing the ammeter. Moreover, you need alligator clips and some wire. As long as you are careful, have the right parts, and have some knowledge about circuits, it is a fairly simple task.

 

How do you put the fob to sleep?

 

While holding down the top (lock) button, double-click the unlock button below it. The light will blink four times to show that the fob has gone to sleep.

I do it regularly when I park overnight in a house driveway, so that the car can't be stolen with a fob relay attack or whatever they call it.

 

Yep, I also have Faraday bags placed around the house. In case the other half doesn't properly put the fob to sleep. All fobs for the other cars are placed in Faraday bags.
I know some people just stick their fobs in the fridge, but the cold messes with the batteries.

 

10/16 build date on my Prime, and the original battery is still going fine. It tests good with an electronic battery tester. I do check the electrolyte levels every year or sooner, and a couple of times a year I put a good charger on it and top off the charge to 14+ volts which may have some equalization effect.