Aux battery caharging

No. When the Prius is IG-OFF, the 12V battery is free to discharge over time and nothing will be done about that.

If your 12V battery is in like-new condition and fully charged, then it can tolerate non-use for 3 weeks. However if the battery has low capacity or is only partially charged, then it is likely you will face a no-start situation on your return, if you do not disconnect the 12V battery before leaving the car.

 

If you have smart key, you should disable it while you are gone. If you are leaving the car at home, a Battery Minder or Battery Tender is a good idea. If you are leaving the car at the airport, then you may want to throw a cheap portable jump starter in the back seat.

 

If you have access to an AC supply when parked get a BatteryMINDer® Plus 12 Volt 1.33 Amp Charger-Maintainer-Conditioner (Desulfator) | All | Battery Chargers by BatteryMINDers.com , hook it up, and then no worries.

JeffD

 

I'm hearing good things about a CTEK charger/maintainer.

Can anyone tell me if it's safe to charge or maintain the Prius 12 volt battery from under the hood?

 

Yes, underhood is safe, but direct connection to the battery is safer.

 

I do it from under the hood every day when I park for the night.I ran a quick connect outside the hood.Makes it easy to plug in. I don't trust that little battery! Hal

 

The CTEK MXS 4003 seems like a viable alternative to a Battery Minder. Just confirm that the model you get does have the desulfation capability ( the 4003 does) to preserve the life of your lead acid battery.

JeffD

 

Why not the CTEK 3300 model?

But I thought I read on the forums about an issue using a battery maintainer connected under the hood might have issues with the cars electronics fooling the charger and therefore losing the benefits of that device.

 

I have my 2006 plugged in when not in use. Still on the original 12v, touch wood!!! Hal

 

I charge mine a couple of times a year with a CTEK 3300 plugged into the Cigarette lighter plug under the dash.

No need to open the hood or the hatch. I just roll the driver's window down and run the ac cord from the wall through the open window with the CTEK 3300 sitting on the driver door armrest and then run the cord to the dash.

The only time I have to do this is when I use the Cigarette lighter plug to run a portable air compressor to add air to the tires as it drains the 12V battery to a level where the car won't start if I don't use the CTEK.

I can offset this partially by leaving the car in Ready Mode while using the compressor but even then the battery gets drained. I just don't drive long mileage trips enough to keep the battery fully charged.

Makes me wish the factory battery was bigger or that the Prius was smart enough to charge the 12V battery more aggressively if it's used primarily for short trips.

 

My 2006 is still on the original 12V, and it never gets plugged in.

Tom

 

Another advantage to leaving the car on (ready) when using the pump is that the pump will run much faster when the car is on because the voltage is higher.

 

Now your making me feel like a wasted all that time plugging in, Tom! Oh well I will continue to do it. Scarred to death of that red triangle! Hal

 

Keeping the battery fully charged is good, so long as the voltage is no more than about 13.6. Higher and you -could- loose water (it vents), and because it's difficult to replace that water, it will shorten the life of the battery.

I have a "Battery Tender", but so far I haven't used it. Now that I'm using Bruiser (2007 FJ Cruiser) in the winter, and Pearl sits for a week at a time or more, I'm going to install that "permanent connection lead" that comes with the Battery Tender under the hood (on the boost point in the fuse box) so I can keep Pearl plugged into the Battery Tender. Last winter the poor battery did run at a lower charge level due to less use. That's not good for it (it could sulphate).

The "de-sulphation" is not really necessary unless you are draining the battery quite low. It won't sulphate unless the charge level gets very low. It won't hurt, it just won't do much.

 

He must have modified the plug to stay energized at all times; otherwise you are quite correct.

 

The 3300 also looks like a good unit for a Prius battery (the previous poster asked about the 4003). These chargers can put out over 1 amp so they can easily handle the small current drain while the Prius is off and still maintain the charge on the battery. It is also important that they are able to break up the sulfate crystals that form on the lead battery plates which are a major cause of lead acid battery life limits.

JeffD

 

We have an Optimate 3+ at our CO home and an Optimate 4 at our AZ home. They are "smart chargers" meaning they test the battery periodically and top it up if it gets low.

We used them during winter storage of our motorcycles for years and now use them on the Prii when we're away for any length of time. They work great - just plug in and forget. You can get them on Amazon for $50 or so.