Using battery maintainer

As far as I know, the 12V in the Prime is the same as the 12V in the Gen 4 Hybrid. It's a standard lead-acid wet cell type (not AGM) under the hood. I would connect the maintainer to the bolts of the terminal connections, just like any other 12V battery.

It's a little late now, but did you have the battery tested before replacing? You might consider getting this https://www.amazon.com/TOPDON-BT100-Automotive-Alternator-Motorcycle to test yourself.

For comparison, the original battery in our 2016 lasted 7 years and died a slow death, meaning it generally started the car just fine, but occasionally toward the end it would not and I had to use a https://www.amazon.com/NOCO-GB40-UltraSafe-Lithium-Starter to power up the car.

 

Nothing unusual. Toyota cautions to remove battery to charge, which I never do.

 

Make sure you get a charger that automatically switches to agm, they’re only about 30 bucks

 

Not enough driving will deteriorate any hybrid 12v

 

It should be, as the original was, but not necessary

 

I’m not sure any will automatically detect and switch to an AGM setting. Our CTEK4.3 has a higher voltage setting, and the manual recommends it for spiral-style AGM’s (the ones that look like a 6-pack). It’ll remember your settings, at least.

Current iteration is CTEK 5 I think. It’s around $80~100.

 

You may be right. I also have a noco genius, and I think I did have to change it manually

 

Are you sure, the Weber Auto video about the 12V battery specifically says it's not a AGM.

That's for the standard Prius, maybe the Prime is different?

 

You could be right. Maybe they saved a few bucks because it was no longer in the cabin

 

Stock 4th Gen battery is conventional battery.

Too, as far as I know, regarding charging an AGM style battery bs conventional: you can never go wrong, charging either kind, as a conventional battery. According to CTEK manuals at least: with spiral wound AGM’s, it’s permissible (and slight advantageous) to charge at a slightly higher voltage. But you don’t want to charge thus with a conventional battery, or even a conventional cased AGM (such as the stock 3rd Gen Yuasa).

in short you can never get into trouble charging as if its conventional lead acid battery.

 

not in a Gen 4, Bisco

 

Andy, I can't think of a reason a 2 year old battery needs to be replaced. Keep an eye on your new one. Dealerships sometimes "fix" things the easy way, and a charging system problem is "fixed" (for a very short time) by putting in a new battery. All this does is gets the owner on their way, but they may soon return. Save your paperwork. If the problem returns, even if you are out of warranty, you notified them of the problem while the car was in warranty but the shop failed to actually find and fix the real problem. The depleted battery may have been merely the symptom of the problem. You do not need a battery maintainer on a car that is driven somewhat regularly.

The 12v battery is recharged while the car is plugged in and the main battery receiving a charge, and while driving from the main battery. The engine doesn't even have an alternator.

The cars do not come with an AGM (absorbed glass mat) battery. They have a standard flooded lead acid battery that needs the electrolyte level checked occasionally and topped off with distilled water as needed. A 100 yen coin held in a pair of pliers is just right to remove the cell caps...although a 25 cent piece works fine. We did replace our 6 year old battery with an AGM battery, and it's working fine, hopefully for many years.

 

This is the battery level since midnight last night.



The car was plugged in since last evening and it was -12°C last night. No preconditioning was used. The battery heater started at 7:33am. From midnight until the battery heater started, the voltage went for 12.51V to 12.47V. once the battery heater started, voltage climbed to 13.55V (I don't know why it dropped to 12.75V at 7:57am though) and stayed until I went for a drive. I can tell the battery heater was on since the green LED in the charge port was lit and this is exactly what the manual says happens when the heater is on and not charging.

While driving, the voltage stayed steady at 14.52V. Where I was when I parked, they have public L2 charger that I used. That's why you see the voltage staying steady at 12.75V there. Then you see my way back followed by a charge at home. Both shows the same 14.52V followed by 12.75V while charging.

Then I went on some errands, during which I didn't charge the car while parked. You can see a lower battery level at around 12.5V while parked. Followed by my drive home and the 12.75V when charging back at home.

So, the 12V battery is charged at three different occasions and at three different voltage levels.

Ready mode/Driving: 14.5V
Battery heater: 13.5V
Charging: 12.75V

It has been consistent for me. Once the temperature gets warm enough that the heater doesn't turn on and I have enough data points, we'll see what's the nightly drain when plugged and unplugged.

I'll also check what happens when preconditioning is happening.

 

Thanks for the info , this confirms that in very cold weather it is important to activate the battery heater and leave the car plugged ...so when it occurs the traction battery gets heated AND the 12V battery gets taken care by the DC to DC converter built in the car charger as indicated by the green LED being on and the car not charging

 

I think a better way to say this is "The 12V battery is recharged whenever the car is in READY." You don't have to be "driving" for the recharge to be taking place.

Also your phrase "from the main battery" is a bit misleading. Whenever a Prius is moving, the main battery is involved, even when the ICE is helping out, too. That's why Toyota calls it Hybrid Synergy Drive.

 

So, preheating also brings the 12V battery to 14.5V so the conditions where the 12V battery is being charged are:

Ready mode/Driving: 14.5V
Preconditioning: 14.5V
Battery heater: 13.5V
Charging: 12.75V

I haven't seen any other occasions yet where the 12V battery was topped off.

BTW, I had the car in On (not Ready or Accessories) last night when setting up the preconditioning time. During that time (about a minute), the voltage dropped to 11.5V. It rapidly climbed back to 12.5V when I turned off the car but it does show that On is a real battery drain.