Low 12-Volt Battery when I start my prius

I am having the same problem as you with the battery. I left of on vacation for about 2 weeks and when I got back into my car I got that low 12V battery message. I’m guessing it’s just time to replace it, but kinda shocked because like yours it’s a 2017. How much did a new replacement battery cost you and where did you get it from? I really don’t want to take it into Toyota, don’t feel like paying $300+ for a battery.

 

Welcome, Christian.

Four years in a hot climate is actually about average for a lead acid battery and I understand it gets pretty hot in Sacramento. But my batteries have tended to last longer even here in Florida. I'm on a 17-day vacation trip with my wife in her '17 Prius Two. We left my Prime home in the garage. It's also a 2017. I popped the hood before we left, but did not put it on a charger. I want to see where the 12V battery charge is when we get home. The Prius seems to have more than typical parasitic draw on the 12V while off. And, if you combine that with short drives that might not have time to fully recharge the battery, it can cause problems.

Even if you haven't been making lots of short trips, I'd still have the battery tested before replacing it. Also, I finally broke down and bought a lithium jump pack battery a couple years ago. I've used it twice so far ....... on other people's cars.

 

Jerry: I've owned our 2 Prii for 10 months, both 2018s. I've never opened up the battery to check fluid level. Have you done this on you other Prii?

 

Most have an AGM type battery that is sealed; no level checking involved.
Recent models went back to the cheaper conventional type located under the hood.
I don't know the model year when that happened.

 

Thanks, Sam.
For sure, neither of mine are AGM. They're under the hood, have slotted caps for removal.
Sigh...until I replace with AGM, I guess I should be checking electrolyte level periodically.

 

i have not heard of anyone doing this. is your electrolyte low?

 

Nope. The Gen 4 and Prime are "Maintenance free." Also, the Gen 4 charges the battery pretty gently. It pumps in about 14.1 volts when you first start, but soon tapers down to about 12.8 or thereabouts. I may get curious and take a look one of these days. I'm a bit of a curious tinkerer. All the other Prii we've had were previous generations and had sealed AGM batteries. No fluid to check in those.

 

Hmm...must have changed over to conventional lead-acid in 2018 Gen 4.

 

All fourth-generation Prius cars, since the introduction in model year 2016, have been built with a flooded lead-acid battery under the hood. As far as I know, all destination markets get the same battery, but the maintenance requirements vary; see my January 2019 posting.

 

Yes, as @Elektroingenieur kindly noted, the change took place with Gen 4 in 2016.

Edit to add that the change was due in large part to the much smaller inverter that freed up space for the battery.

 

Just added some distilled water to our 2018 Prius 2 battery. No cells were dry, but one of them took more water than the other 5. FYI, I filled each cell until the surface of the electrolyte was touching the "tube", which causes the fluid surface to cup slightly.
I assume this decades-old method is still used.

So, Jerry, you might want to edit your post #28.

 

Too late now to edit it. But I appreciate you letting us know what you found and did. AFAIK, your fill method is the correct one. I'll take a look at both of ours when we get home this coming weekend.

 

"Maintenance free" lead acid batteries are designed not to lose water, so they shouldn't need topping up. You can add water, but you shouldn't need to for the life of the battery unless something goes wrong. They might not be designed to give you easy access to the cells. But it is clear from all the 12V battery posts that something often goes wrong with Prius batteries.

The first page of this paper has a short explanation. Sealed maintenance-free lead/acid batteries: Properties and application of a new battery generation - ScienceDirect
In addition to the electrode chemistry the paper mentions, I think they also have some kind of catalyst to recombine lost gasses back into water.

I miss the original, made in Japan, Panasonic battery in my Toyota 4Runner. Mine lasted something like 11 years and was just getting to be marginal when I replaced it. There are lots of reports of them going 10+ years. It was made of translucent plastic, so you could shine a light through and check the electrolyte level. None of the replacement batteries on the market come close (they are all made by three or four manufacturers, no matter what store slaps a label on it). Obviously that's much heavier than a Prius battery, but it's too bad they couldn't use the same technology on a smaller scale.

 

Our 2002 Chrysler 300M had a maintenance-free battery mounted just in front of the front passenger-side wheel and completely inaccessible, so there was no way to top it up or even check it. I replaced it when it was seven years old only because winter was approaching and I didn't want anyone to get stranded with a bad battery.

 

The PRIUS Battery is see-through - you can see the level. Plus it's got removable caps. I've never checked mine (have on previous cars) - but the caps certainly look like they've been off - must be in service.



Maybe I should have a closer look?

 

I'll post my experience with this problem as I suspect there might be many worldwide who are experiencing issues under Covid travel restrictions.

I have a Gen4 2016 model, based in the UK. I upgraded from the Gen3 model and 'yes', the 12V battery was moved up into the main engine compartment from the rear boot (trunk) at that time. So, it is now much easier to access, like a 'normal' car! Mine in the UK looks the same as the photos from Australia above, so that all fits in with Elektroingenieur's postings earlier. My caps don't look like they have been taken off (the car has completed 3 standard annual services with Toyota).

My personal experience with the 'parasitic drain' in the Gen4, when the car is left unused, seems to be more of a problem than with the Gen3 or Gen2. My experience with these earlier models was that I could comfortably go for a 3 - 4 week holiday (vacation) and start the car without problem. Perhaps I was lucky.

With this Gen4, I have managed up to 25 days with the car left unlocked in the garage. However, last year I went away for 21 days and locked the car. Came back to a low battery warning and the car unable to start. This would pose a problem if left at an airport car park for example.

I decided to just trickle charge the 12V overnight and had no further problems over the last winter and through this year (11 months later). In the meantime, I also purchased a portable battery jumpstarter as a backup plan to secure me through last winter (a Suaoki U3). As I should have expected after buying anything as a backup, I didn't need it!

...until this week. I had been away for 2 weeks, but got caught with an additional 2 weeks quarantine on my return after new Covid rules were imposed while we are travelling. I had left the car unlocked this time. After 31 days, I could see the interior lights were still coming on, so I thought I was in luck. Alas, no. The MFD flashed up for second then all went blank.

The Suaoki U3 worked a treat. As soon as it was connected up, all the car lights and MFD came on. The car started as if nothing had happened and there were no error codes. I learnt two things. First, the jumpstarter still had more than 50-75% of its charge left after not being used for 11 months. Secondly, as the design of the Prius is such that all the hard work of turning the ICE is done by the traction battery, the 'jump start' only needed minimal power. The charge indicator on the Suaoki unit looked the same before and after the 'jump'. For a unit that is about the size of a slightly bulky looking Kindle, and competitively priced, this left me quite impressed. One limitation is that it can't be used as a trickle charger. It will do a 'jump', and it has a built in LED torch/stobe with a USB port so it can double as an ordinary battery pack for devices.

I'm guessing most people here will be aware of the 'parasitic drain'. I thought leaving the car unlocked would make a big difference, but it looks like it may only have gained me a few days. I understand the SKS system still polls for the key fob, so this may be another factor. My keys were left about 4m (12 - 14 ft) from the car, and I'm not sure if that eliminates it.

Is the general view here that I should not even be expecting being able to leave the car for a month without setting up a trickle charger?

 

I would expect a "normal" car to last at least a month and still start. It's not uncommon to go away for 4 weeks.

It might be worth measuring the parasitic drain to see if it's unusually high in the Prius. Or to see how much of a difference SKS makes (it can be disabled with Carista), or how much difference having it plugged in makes. Maybe someone has already tested it?

I bought a lithium jump starter, and it discharged itself from full to nearly empty in a few months. Not great for something that I'm likely to rarely use. I have yet to find a brand that's well-engineered, high quality, and reliable. I'm extremely skeptical of all the no-name brands because jump starting is extremely abusive to lithium batteries.

There is a combination of buttons you can press on the key to disable the key from being picked up by the car. Hold lock while pressing unlock twice. The red light will blink a few times in a pattern if successful. It saves battery on the key and stops it from being found by the car, but it doesn't stop the car from continuously searching for keys. It might save power on the car if the key is just close enough to be in range.

 

Very useful thoughts, thank you. I did wonder whether the SKS current drain in the car was greater if it was 'searching for' the key or if it 'found' the key; or indeed it there was no significant difference between these states.

As you say, if it is the former, it would be theoretically better to leave the keys close to or even inside the car and not disabled (security issues permitting).

I am guessing there is no way to know apart from trial and error?

 

You can check parasitic drain, with a multimeter in series, say between neg cable and car body (or engine). Set the scale first to amps, then milliamps. With our 3rd Gen I measured 16~18 milliamperes with sporadic spikes (maybe every 6 sec) to around 40.

With regular batteries I found pulling it right out, around the 3 year mark, was a good opportunity to clean clamps/posts and verify levels (with a good back light) and top up to the top line. Typical battery has two such lines, like a dipstick.

Every MINUTE the car is off is draining the battery. Maybe overkill, but having a garage, I plug in a smart charger any day the car won't be used, and leave it on till next use.