How long will 12v battery last between drives?

The 12V battery in the Gen 4 is much bigger than the battery that you had in the '05. You shouldn't have any problem if you only use the car every two weeks

 

That really depends on a lot of variables. Temperature and age of the battery have a lot to do with how long any battery lasts and 12V batteries are no different. For extended storage, it's recommended to disconnect the battery so that you aren't draining it.

 

Found this battery drain calculation that might be helpful for you. Leaving a Toyota Prius Undriven

A month is probably pushing it if you're not disconnecting the battery.

 

Too many unknowns to give a good answer.

IF.....it was fully charged going in, then yes.

BUT.....the system is not known to keep the 12 V at a really full charge.
AND.....if when you do use it, your trips are less than 30 miles or so.....then it is more likely not to be fully charged.

You really should get a tender type small automatic battery charger and connect it overnight every couple of weeks.
IF....you connect it after 2 weeks and the green light comes on after less than an hour, that is a good indication that it would go a month.

Or leave it connected all the time.
They can be had at WalMart and all auto parts stores for around $25.

Anything labeled as a "trickle charger" is NOT the same thing.

 

my 6 year old smaller battery has sat for 2 months in an unheated garage every year since new, but heat may be harder on it, idk.

 

In the Owner’s Manual (PDF), on page 80, Toyota advises to “drive the vehicle at least once every few months for at least 30 minutes or 10 miles (16 km),” to keep the hybrid battery charged. Page 710 says the 12-volt battery will also discharge after an unspecified “long time.”

I’ve written before, in these threads, about Toyota’s recommendations to dealers on maintaining the batteries on new vehicles in inventory and how the car makes a record when it isn’t operated for more than 60 days:

• Charge auxillary battery without driving | PriusChat
• Leaving vehicle for vacation | PriusChat

 

Bear in mind that that article was about 15 years ago - and 2 generations of PRIUS - possibly still relevant, but who knows?

 

Results from 2019 Shutdown for 24 days-- It was seamless!

In a nutshell, the 12V battery was disconnected, charged, and left on open-circuit for 24 days. Upon return the open-circuit voltage had declined from 12.68VDC to 12.48VDC. Once the battery was reconnected, without any charging, the Prius achieved a READY light and started on first attempt. The only initialization step that was required was to set the Date and Clock. I am very pleased!!!
(This is a 2018 Prius, GEN4, with 13000 miles. HV battery (traction battery) indicated 3/4 charge both before and after shutdown. The car was garaged at about 50F.)

Dec: 2019 Shutdown for 24 days

Begin by preparing the car: See Owners Manual pp729 through 733. All of it.
There will be initializations required upon reconnect because everything stored in the ECU is lost. Pp780

• Make sure the HV battery is pretty well charged. I'd like 80% or better.
• Doors unlocked...in my case, because its is garaged.
• Power EVERYTHING down
  • Engine, of course - OFF
  • Lights - OFF
  • Audio - OFF
  • HVAC - OFF
  • Nothing plugged into outlets or USB.
• Lift the NEGATIVE (-) terminal first, pp 733.
• Lift the POSITIVE (+) terminal
• Measure the battery voltage:
  Time:__13:03_____ __12.65__________VDC
  
• After 1 hour measure again:
  Time:__13:54_____ ___12.56__________VDC
  
  
  
• Put the battery on SLOW charge, 2A, for a number of hours…..6 in this case.
• Disconnect the battery:
  
  Time:__18:30_____ __13.25_________VDC
  After several hours:
  Time:__22:45_____ __12.68_________VDC

Upon Return:
Begin by documenting the event for future reference:

• Date and time to start-up:
  Date:__1/9/2019________
  
  Pre-startup or charge voltage:
  Time:__13:05___ __12.48____________VDC
  
  
• If the voltage is <12V consider charging before reinstallation. Was not required....
• Clean the battery terminals
• Reconnect battery cables: Reconnect POSITIVE (+) terminal first, followed by NEGATIVE (-)
• Attempt to achieve READY condition to start the vehicle. See pp 732 for possible startup issues. The doors may not unlock. It may take two or three attempts to get the READY light.
• Reset DATE and TIME if prompted. I was prompted by the vehicle for date but not time.
• After restart several systems require initialization: pp 780. These are not a big deal. It will be interesting to see if my customizations will stick along with radio presets, etc. Radio presets good, maintenance times good, customization features....still customized. It all seems to be in non-volatile memory. Great!

 

Why did you remove both terminals? Whenever I've "stored" a car, I've only removed the negative.

 

Just to ensure open circuit on the battery. This leaves no path for leakage currents. It also allows me to clean the terminals and area under the cable/connectors as I should do regularly.

 

If you didn't disconnect the battery, and had a protracted period, a week, or two, or three, the outcome might be different. Even if the car starts, it's taken a hit.

Any time ours sits for multiple days, I hook up a smart charger, and leave it on. Sometimes overkill, for short duration downtime, no matter. This isn't practical for all owners though, say street street parkers.

There's a constant low level drain on the battery, to maintain settings, detect fob. That maybe changing though: there's some clues on the fourth gen Manual, hint at some permanent memory, maybe a built-in flash drive??

 

All I can tell you is that I've had good success with this procedure in the past on 4Runners and my GEN 3 Prius. (Yes my 2002 4Runner had the same treatment during this period but it lost the radio setup...as always. Here, the Prius is more sophisticated.) It seems that there has been considerable conjecture on this topic in this and other forums so I took the time to document this event for others to consider. After all, the condition of the 12V battery on open-circuit is exactly the same as a new battery prepared for sale. I'm pretty comfortable with this as I did spend an entire week in the US Navy submarine battery school. One important learning from that experience is that surface cleanliness is mandatory to eliminate surface leakage currents and I recommend this prior to the charging step. So, I lift both leads, tie-wrap the connectors away from the terminals, and its all good for....well 24 days.

 

Yes, people tend to forget about cleaning the actual surface of the battery when they clean the terminals, IIRC the small surface current leakages were known as corona discharge when I was on a motor vehicle electrics course back in the 80s.

 

(Edit: I now see that I gave basically this same advice already......but it bears repeating.)

Maybe. But as it ages, maybe not.

The best plan it to spend ~ $30 on a small battery maintainer (tender) and connect it for 12 hours every two weeks or so.
Or leave it connected all the time. They are designed specifically to do that.
That does NOT mean a cheap trickle charger.

Starting a vehicle without actually driving it is NOT a good idea.
You might keep your 12 V battery up by doing that.......at the expense of water accumulating in your exhaust and crankcase.
If you won't be driving, it is better to leave it OFF.

 

Amplifiers work by induction, a tiny signal is amplified, well if the positive is hooked up, any positive wire will conduct to a negative wire, be it ever so humble.
When I'm doing a hard reboot I remove the positive terminal for 10 minutes, the netative can stay, if I were storing or not using for a month I would unhook both positive and negative and I'd cover the positive terminal with something.

 

Yup, instead of playing this "how low can it go" game.

I appreciate for someone street parked, or in a condo parking lot with no electrical outlets, this is not going to fly.

 

No it doesn't......and no it won't.
If the "negative" wires have no return path to the voltage source, then no conduction will occur.

 

While working from home in San Diego during the Covid-19 "shelter in place" order, my 2017 Prius Prime auxiliary battery went dead, to the point I couldn't open the doors using the key fob. It was only 2 weeks ! I have a solar battery tender, but I didn't use it because it was not expected to go dead after only 2 weeks. Lessons learned...always use the solar charger, for even one week of non-use.