Gen 4 12 Volt battery.

I purchased a battery maintainer/charger after recommendation on this forum for my car during lockdown as I was worried about it going flat and it has worked a treat. I just hooked it up and left it on all the time to do its thing. I kept the 12v battery connected the whole time.

Now I am using my car more I haven't worried about using the charger and everything has been good. Before I purchased the charger I was getting pretty low readings, but I never had any problems starting. After using the maintainer/charger for a couple of weeks my readings went back up and stayed there.

 

So I just came back from a 24hr 2amp trickle charge with a Schumacher model se 10-52. Not sure if this is too long or not long enough. Battery was 12.2V coming off the charger. Then I turned on headlights for 30 seconds, turned off and battery is now at about 11.9V.

 

That's not good. Get it electronic load tested, or just replace, before winter.

 

The only time I ever removed a battery to charge it was when it was 30 degrees below zero and I had to take it inside to get it warm enough to take a charge. (Obviously, before we moved to Florida. )

 

Another reason to remove the battery: if you're an apartment dweller, with no access to 120 volt outlet where you're parked. But yeah, other than practicalities, no need to remove the battery.

 

Doesn't Prime use the traction (hybrid) battery to start/crank the engine, not the 12V battery?

 

Yup. Just like all Prii. But it does use the 12V to connect the traction battery to the car so it can crank the engine. So, there's starting the car and starting the engine, separate but related.

 

I installed that model today in my 2017 prime advanced. Physically, it's a perfect clone of the stock battery. It's maintenance free. No problems installing or using it for 30 miles of freeway / city driving.

The CCA is slightly different but not enough to impact the car.

Background: I replaced the battery because I've been using the car abnormally for the last few months and it failed to start a couple days ago. I've had the car for a year, and charge it daily. Since the pandemic I don't drive it long distances and found myself with a full gas tank that was 11 months old. This is not a good thing as gas can go bad. To burn off the gas I stopped charging it and have run it in "charge mode" daily for the last couple months. I'm finally down to 1/2 tank. I should be able to add Stabil and a half tank of fresh gas now.

When the car failed to start it had been sitting for a week. I checked the battery and found it was quite low, around 7 volts or so. I used a battery charger to jump it, and it took a charge instantly. I drove it for half hour or so. It read over 12.5v when I parked it for the night. The next morning I checked and found the voltage was just above 11 volts. That indicates a bad cell.

Here's the funny thing; When I found it was low this morning I plugged in the 220v charger for the traction pack. The volt meter immediately showed that the 12V battery was charging.

What I think happened; I bought the car used from a Volkswagon dealer. They had it in inventory for a few months. My Toyota dealer told me that the VW dealer (a sister company) brought my car in to get the battery checked because it was dead. They charged it and gave it an "OK" diagnostic. It went back on the lot. I suspect that the battery was marginal, but that never showed up as a problem because I was charging the car every night. Once I stopped the nightly charge the voltage dropped due to the bad battery and all the electrical loads on it when it's turned off.

Dan

 

That could very well be what happened. The Prime and the PiP both maintain the 12V while charging the traction battery. Keep in mind, though, that when the Prime is not charging but the EVSE cable is still plugged into the car's charging port, it's putting a small load on the 12V system, so that's why the manual advises not leaving the car plugged in long term.

 

When I brought my brand new 2021 Limited home from the dealership two and a half weeks ago I set in to checking all sorts of things. I've determined that the dealer prep was rather inadequate and I'll mention that at my first service. My experience with two previous Prius vehicles has already accustomed me to keeping a close eye on the 12 V battery health. After topping up the inverter coolant and bringing the tire pressures up to the recommended 36 front 35 rear, I did a spot check with my DVOM on the 12 V battery. I left the battery connected and in place, and it had been a couple hours since the vehicle was run. Measured 12.4 volts, which in my experience indicates a state of charge maybe around 68%. There is likely some draw from the battery from various systems that are operational while the vehicle is off, but this reading seemed a bit low. I hadn't read in the owners manual yet about battery maintenance so I held off on getting my battery maintainer out just yet. I wasn't sure what might be erased if the 12 V was disconnected, so I didn't check the unconnected voltage either. Drove back and forth to work (140 miles round trip) for a week and read some more in the owner's manual. Toyota recommends disconnecting the battery negative lead for charging. The next weekend I disconnected both + and - battery connections and hooked up my maintainer. It ran through various checks and eventually reported a good battery after about 2 hours. I probably should have checked the voltage at that time, but didn't. Just hooked it all back up and cycled it until I could make it ready. I have a USB charging adapter plugged into the 12 V socket in the center console and it has a digital display of voltage which I monitor. Drove the vehicle for another week and noticed that sometimes while driving the displayed voltage was reading 12.4 volts. I usually check the readout after starting and it always reads around 14.4 volts, so now this is something else to wonder about. Previous Prius would always read 14.4 volts continuously when made ready. Electrolyte levels are fine (quarter turn with a real quarter opens the cell) and two weeks of driving should have brought a battery in need of charging back up to proper voltage. Long story short, I might be making an early appointment to have the battery checked if I see anymore low voltage readings.

 

@AzWxGuy you don’t need to disconnect 12 volt before charging. I know the Owners Manual cautions to do this; I do it all the time. Ours is hooked up right now, has been for a couple of days.

A battery that reads 12.4 just a couple of hours after driving, will likely be at 12.2~12.3 by the next morning.

 

Did you have a Gen 4 before? There are some significant changes from Gen 2 and 3 - the battery is a different type, and the way the car handles charging is different.

I've had mine 4 3/4 years - never looked at the battery, and it's going fine. I'm doing a lot less driving since COVID lockdown, sometimes it's idle for 4 or 5 days - never had a problem.

I'd stop worrying about it - check it in 5 years.

Professor John Kelly put together a great video on it - just check that it starts at the beginning - it kept starting partway through.

 

There are a couple reasons I took the battery out of the circuit. My Optimate 5 conditioner will charge the battery while monitoring current flow to reduce the battery's current demand below 400mA at 13.6V which would be consistent with a battery that has accepted as much charge as its basic condition allows. As long as there is a parasitic draw from vehicle systems the charge verification cycle will never complete. Also, this conditioner will test for and correct problems with sulphation which I doubt is an issue with a new battery. But the voltage retention test, which detects and corrects sulphation, won't complete if the battery is connected to the vehicle. I can confirm that the radio channel settings are non-volatile in this iteration of Prius, as well as the power window auto settings. I didn't check the trip settings to see if they reset though.

 

This is my first Gen 4, consistent with my car history in my signature. Yes, I am aware of the differences between this generation and the previous. Plenty of great information from this thread and others. I watched the Professor John Kelly video before I purchased my 2021 during my study of the Gen 4 forum. Great stuff. I'm only slightly concerned about my 12 V health, given what I have observed. I'll probably run another cycle with my battery maintainer and remember to check the voltage after completion. That is the only answer I don't have yet.

 

What @alanclarkeau said. +1

Every six months or so, I'll check my 12V. It usually reads about 12.4V. I've concluded that that's where the car likes to keep it. I also have a USB adapter with voltage monitor which also varies (on the rare times I think to look at it) between 14.1 at startup and somewhere in the mid 12s once the car is satisfied with the charge level.

I'm not at all concerned about my 4+ year old battery, so I for sure wouldn't worry about a new one.

 

These are the most likely reasons that they recommend removing the battery from the circuit. Many of the modern battery chargers do more than just supplying a straight DC voltage. There's no telling what odd high freq stuff is being injected on top of the 12 volts to do things like desulfate. It's hard to guard the inverter and internal system against deliberate application of odd voltages. It's easier to just tell people not to charge it while it's hooked up.

 

Isn't it possible that keeping the battery fully charged at all times reduces the risk of damage? Our Gen 2 has a 5 year old 12V, and with 291k miles on the car's odometer, I do not plan to replace the battery. If the battery dies, that will be it for the car. For the last year or so, the charger/maintainer has only been removed from the car when it is being driven. I also happen to think something is more likely to go wrong removing the battery multiple times to charge it than not, and having to reset the things that need to be reset multiple times also makes it not worth doing.

 

Yes, keeping it charged with a simple battery maintainer (we used to call them trickle chargers) would pose minimal risk to the battery and the car's systems. On my last car (2002 Prius) I wired a 1.5 watt solar battery maintainer to the battery and left that in the back window. It worked perfectly for more than 10 years.

Unfortunately I don't have a place that I can do that with my current model. Tinted windows make an 'in car' solar charger ineffective.

Dan

 

Thanks for the post, and allaying my fears. I'm still a little sensitive after years and years of closely monitoring AGM batteries in my previous Prius vehicles. Time to relax and just drive the car.

 

Yup. It shouldn't be stressful. I keep a lithium jump pack in the car with me. I've used it twice ... but never on my own car. Still, you never know when you might leave your dome light on while away from home.