running AC overnight drops battery level a lot...

[JennyJ]

Hey there!  The other night I tried sleeping in my 2007 Prius in the driveway with the AC on for the first time.


The battery level started at its usual six bars, then dropped to two bars fairly quickly when AC turned on. It stayed at 2 bars, which was alarming as the last time I've seen it that low was chugging up the side of a WV mountain.


Is it normal for levels to drop that low?  The next morning the battery recharged okay with driving, but seemed unhappy the rest of the day, with levels dropping and recharging frequently. Today it's behaving more as usual.

Am I right to be concerned/alarmed? how many bars do you Prius owners usually see while running AC at night?

 

[JerryJ]

I'm a fairly new Prius owner myself, but from what I've read that is exactly how it should behave. The engine will wait till the battery is in the last blue bar or the first purple bar to kick on, and only run long enough to raise it one or two bars, then repeats the cycle as needed. The regenerative braking is why your battery is often much higher in charge, the Prius computers only put it into charging mode when necessary.

The Prius battery doesn't wear down from not being fully charged like a standard car battery does, and has the longest life when kept between 40-80% charged. Purple bars are actually around 50% charge, green bars at the top are 80-90% charge. It almost never gets to 100%, and the system will shut down before it gets so low it is damaged. Most damage to a Prius battery comes from heat and corrosion (most common blocks in the battery to fail are the ones in the middle due to high temps).

I highly recommend getting a Veepeak OBD2 Bluetooth adaptor (different ones for Android vs Apple phones, so read description). Once it arrives, you plug it into the OBD2 port under the right side of the drivers side dashboard. Download the Dr Prius app, and use it to check your battery from time to time. Check the Priuschat.com forums for details on how to use it (very easy). It can also read diagnostic trouble codes if you ever have ANY issues with your Prius (use those codes and Priuschat forums to make sure mechanics/dealerships aren't ripping you off).

 

[JennyJ]

Thanks, Jerry!  So it's normal to have only two bars while AC is running overnight. Good to know.

I've had the car for five years and usually drive with the energy monitor on. It never drops below 6 bars unless I turn on the AC to avoid fumes while stuck in hot summer traffic... and when it does drop significantly, I freak out and shut off the AC, worrying I'm damaging the battery somehow, because....

My very first month I got a Triangle of Death while driving to Florida on I-75 in fairly heavy traffic through remote Georgia, heading for a gas fill-up some five miles away. Suddenly, a buzzer started blaring and what seemed like 100 warning signs flashed like crazy before the car shut down with barely enough motion to limp to the shoulder. I sat there trembling, frightened to death as cars whizzed by, thinking, "I ~hate~ this car!!!"  lol

After 15 minutes I tried starting the car again, then cautiously drove to the next station, terrified the car was going to blow up. I continued being terrified for the rest of the trip of getting another warning.

Fortunately, it never happened again. But the other day I discovered that the Triangle of Death had probably been triggered by letting the gas tank get too low.... seems the gas gauge isn't accurate at low levels and I was probably nearly out of gas.

So, yeah, even after five years I continually worry that I'm damaging the car somehow... the Prius is a lot more complicated than all my gas-engine cars were. LOL!

 

[JerryJ]

I agree, a Prius definitely takes getting used to! When I went to test drive it, I turned it on and off three times before the salesman let me know it was on even though the engine wasn't.

I wouldn't be so nervous about using the ac, it's actually good for the battery. The battery is cooled by air from inside the car entering thru the vent next to the rear passenger seat. The cooler the ac makes that air, the cooler the battery.

That triangle of death in heavy Georgia traffic may have been the low gas, or it may have been a hot battery, or several other possibilities. Getting that OBD2 adaptor I mentioned before will help you diagnose events like that in the future (and many error codes are stored, so it could help diagnose the past as well).

 

[ByeBye]

JerryJ...JennyJ
Both have Prius...what are the odds?!?!

 

[JerryJ]

I noticed that too!  

 

[JennyJ]

I got a chuckle out of our names too!

The other day I saw a Prius V online and wondered if it might not be a better car for me, roomier, etc. So today I took one at a local used-car dealer for a drive, a 2015 Prius v 5, 71K miles for $15,300.  What a difference! Bigger and more solid-feeling, very comfy to drive, and no blind spots like my 2007... so tempting!

I saw another car online a little while ago, a 2015 V3 with 80k miles for $12,200, rather more affordable.   Now I'm all conflicted. lol

 

[JerryJ]

I'm not sure what the difference is between V3 and V5 trim packages, but I doubt it's a $3100 difference.

Either way, I'm sure you'll be happy with the extra space. At that price point, I would definitely have it checked by a good mechanic first. Many reputable mechanics will do a thorough inspection for $50-100, which is well worth it when spending over $10k!

 

[JennyJ]

Thanks, Jerry... lots to think about!

Drove the 2012 yesterday and was unimpressed. I like the 2015 much better... I just need to decide whether I really want to pay so much for more room, heh.

Maybe I should just keep the 2007 and add a hitch + cargo box for more storage? https://www.amazon.com/gp/product/B00JF53ZEE