12v battery maintenance when Prius is not driven for several days

There was a 12v battery thread recently - 12v battery voltage? | PriusChat

Might give you some idea of other's thoughts.

There's also Weber Automotive's informative YouTube -

worth listening to.

 

I doubt it.

There's no way for the 12V battery to charge the HV, so nothing happens from that perspective, but the HV does charge the 12V when the car is in Ready mode. While this will discharge the HV battery a bit more quickly (once), which you may think will reduce its life (rechargeable batteries have a limited number of charge/discharge cycles), in reality the ICE kicks in when the HV gets down to around 2 bars and then the MG takes the electrical strain. If the 12V didn't need charging, that same HV energy would be used to power the motor a few seconds longer. So really, all that happens is you use a bit more fuel a little bit earlier, and the HV gets the same use.

Low 12V voltage can cause all sorts of issues indirectly though. Error codes are a common one.

 

Our '08 with it's original OEM battery went 3 weeks in summer when we were on vac.

NO problems.

 

a battery maintainer is a good idea if you only drive a couple days a week. for prolonged periods of downtime, turn off sks on your fob.
reducing hv battery life is nonsense

 

he's half right, and half clueless. that's more dangerous than completely wrong

never a bad idea to use a maintainer. make sure the one from your tractor is appropriate for prius battery, it is special. and fragile

 

of course there is drain, electronics are on all the time. you need the spec to make sure the drain isn't above that

 

same here. 6-8 weeks every winter for the last 6 years

 

Absolute total BS.
The HV battery does NOTHING while the car is OFF; thus it doesn't care what condition the 12 V is in.

A cheap trickle charger is a BAD idea. A good automatic battery maintainer is a good idea but is only necessary if the car sits for a LONG time, like two weeks or more. If the 12 V won't hold up for 2 weeks, it is going bad already.

That guy is a total moron. Most of what he says is just made up.
I hope the whole shop isn't like that.

 

12V and hybrid batteries are completely separate. When the car is off, the hybrid battery is disconnected electrically by a set of heavy duty contacters. It basically does nothing when the car is off and is separted from any circuitry by air gaps (contacters). It is therefore impossible for the 12V battery to effect the hybrid battery when the car is off. To suggest otherwise is utter nonsense. There is no high voltage from the hybrid battery anywhere in the car when it's off. Period. You can probably help your 12V battery a bit by using an appropriate charger/maintainer, but it will do absolutely nothing for your hybrid battery.

 

There is no reason to think that the electronics that needs to be "kept alive" while the car is OFF in a Prius is much, or any, different than a conventional car. The electronics needed to RUN it might be more but given all of the electronic controls in "conventional" cars now even that is suspect.

The main reason that the Prius appears to discharge the battery quicker in storage is: The battery is much smaller than a vehicle with a conventional 12 V starter.

EVERYTHING he said are conclusions arrived at by not understanding anything about the evidence that he has seen. He is trying to impress you with his knowledge.......and is doing exactly to opposite.

 

It was rather harsh, but it was also correct. This service manager doesn't know what he's talking about. As you've already learned, the car can sit for weeks and weeks without being driven and have no problems unless that 12V is already approaching the end of its service life. We've left my wife's '07 for weeks at a time while on trips in my car. Come back and it starts right up.

And the HV battery is so much bigger than the 12V that the extra load of charging a low 12V is nothing. Compare that to the traction battery starting the engine by spinning it up to 1,000 rpm until it makes oil pressure before the ignition and fuel come on. And it does that every time you stop or even go really slowly. Drop in the bucket.

Once again, the Prius mantra applies. "Just drive it."

 

When my Gen 2 was in an accident, it sat in the summer sun under 110 degree heat daily for 2 weeks or so. Started up no problem. But then again, I had an Optima in it.

 

@n4in We are low usage, ours (3rd gen) sits idle often for 2~4 days. Whenever the car will not be used a particular day, I hook up a CTEK 4.3, let it run through it's charging cycle, and leave it connected, until the next time the car is used. Might be overkill, but it's working for me.

I've measure battery drain on ours: it's roughly 18 miliamperes constantly, with spikes to around 40 every 5~10 seconds.