Keeping Aux. Battery Charged During Long Storage

I use a VDC Battery Minder on my Prius, actually on all of my equipment. It's probably better to hook directly to the battery. There might be enough voltage drop between the jump start post and the battery, the tender might be fooled into providing too much current

 

I've been gone 5-6 weeks and did not experience any battery problems upon my return. Of course with your 2004, you *could* be approaching the end of the 12v battery's life.

 

Correct, the VDC Battery Minder is considered a float charger. It's not a battery charger, indeed, if the battery voltage is <10, it will refuse to work at all

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I have six of these in use at my home and my hobby farm. The equipment at my hobby farm can sit up to half a year, this is the only way to properly charge and maintain batteries

I did post photos of my installation, but the photos are on my computer at home. I'm sure if you search the site, you'll come across the photos I took of the ring terminals - supplied by VDC - that I hooked up to the battery.

It was a fairly simple install. Assuming you can park in a garage, you don't have to worry about the unit getting wet. It's not meant for outdoor use

 

I need help! I travel for a living and find that every time I come home my battery is dead. I did ask the question when I bought my Prius and was told the battery would hold a charge for about 30 days. None of the Toyota Prius mechanics seem to have a solution for my problem. What can I do to keep my battery charged while I'm away? It is dead after 3 or 4 days and my car is a 2007. Any ideas?

 

Hi Jill,

If you park in a garage and have an AC outlet available, then I suggest you obtain and use a float charger as Jay described in post #5 above.

The Toyota TSB that discusses battery maintenance suggests that the 12V auxiliary battery must be charged once every 10 days by making the Prius READY for 30 minutes or longer.

If you are unable to use a float charger, an alternative would be to ensure the battery is fully charged before storage, then disconnect the negative battery cable at the battery (or at the body of the car) or else disconnect the positive cable at the dedicated jumpstart terminal within the main relay/fuse box near the inverter. However this approach requires access to simple metric tools. Further the electronic hatch release will not function without 12V power so you must crawl into the hatch from the rear seat and find the mechanical hatch release, if you had previously disconnected a battery cable and subsequently need to access the hatch.

 

Thanks I just printed off the "Batteryminder" info so I can look into it tomorrow. Toyota says that continuing to jumpstart my Prius will damage the battery but so far if I'm gone for just a few days it goes dead. Seems crazy that I have to drive the hell out of my car between jobs to keep the battery charged. Last time I even had them charge it up at the dealership and it still died in a week. Pretty frustrating! Thanks for your input, I will check it out.

 

Hi Jill,

It's not the actual jumpstart that damages the battery, but rather the fact that the battery is allowed to discharge to the point where a jumpstart is required. If the battery was fully-charged and still died within a week of the charge, then I would say you need a new 12V auxiliary battery. Then use the float charger with the new battery to keep it charged and ready to go when you return home from your travels.

 

Once a 12V has been run low enough to require a jump, you need to plan to replace it. They will not have the same capacity in the future and the problems will become more frequent. My last Tundra battery lasted only 2 years (on a 72 month battery)--it had a deep discharge last winter during a spell of short, cold drives and I had a difficult time recharging it. When the cool weather began this fall it had enough and wasn't worth messing with, besides the replacement was free.

If your vehicle has a dealer installed alarm they are known to cause battery drain.

There is a thread somewhere about replacement 12V batteries that has a recommended aftermarket that is supposed to be both less expensive, and have more capacity.

 

So the fact that my battery went dead the first time only a week after I bought the car means that my battery was pretty low when I bought it. Seems like it should have been fully charged before I drove off the lot with it. I did feel like everytime I charged it up it lasted fewer days. Hard to believe that I have to replace the battery after 1 1/2 years.

 

If you drove your car during that time and it went dead only a week after you bought the car, that was probably a bad battery from the start, assuming nothing was left on to cause it to die. As was mentioned above, once a battery is allowed to discharge to the point a jump start is required it has been weakened irreversibly and will fail much sooner than if it had not suffered such a discharge event. Since you live in a relatively mild climate, I would think your battery should last for at least the length of the basic warranty period of 36 months unless it was defective from the beginning or subjected to an accidental discharge from leaving the interior lights on. If you bought your car new and you can document the troubles you've been having for an extended period, I'd try to get Toyota to cover at least part of a new battery under warranty.

Many people have left their Prius for extended periods and haven't had any problems, but with a weakened battery or very low temperatures a jump start is more likely to be needed. This was my low cost solution to the discharge problem with a car that sits for long periods:

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Hi Jill,

Yes, the Prius pre-delivery instructions require the dealer to fully charge the 12V auxiliary battery before delivery to the customer. If the battery died so quickly then that was not done, or else the battery had already become weak while the dealer owned the car.

I suggest you inquire into the possibility of having the 12V battery replaced under warranty, or else buy a replacement if necessary.

How many miles do you drive the car monthly?

 

I don't drive it too much, some months I'm only home 10 days and some months 3 weeks so it varies. I've had it for a year and a half and it still only has about 8000 miles on it. The thing that gets me is that I did ask the question when I bought the car and was told that I wouldn't have this problem. Everytime I ask someone at Toyota they have a different response, even within the same dealership. It sounds like I need to have my battery replaced and then get this batteryminder thing as it will just happen again the next time I go away.

 

Does it matter which battery you hook the batteryminder up to?

 

Only the 12 vdc battery. Never ever to the 200 vdc traction battery

 

Hi Jill,

Yes, if you ask the salesrep s/he is not going to say anything to hamper the sale.

I've attached TSB PG007-03 that relates to this issue so that you can become an expert on the topic and know more (actually that won't be hard to do) than the dealership staff that you've been speaking with.

 

Okay! I'm gonna study and learn!! I spoke to the guy today and he said to pull out the dome circut and that would do the same? I've heard that before but haven't tried it yet. What do you think?

 

Hi Jill,

I am providing another TSB since it sounds like you are an interested student. TSB PD102-06 provides pre-delivery instructions for the Toyota tech who is getting a new Prius ready for sale.

This is relevant to your question because yes, the DOME fuse is not installed when the Prius is shipped from Japan. However, 12V power is still available to some of the ECUs.

Note page 3 of the TSB which provides the pre-delivery checklist, item B11. Three DTC will be logged that have to do with the Body ECU, Smart ECU, and Combination Meter ECU. So if you just pull the DOME fuse, those DTC will be logged and will have to be cleared when you are ready to bring the car out of storage (which you can do by disconnecting the negative 12V battery terminal for a few minutes, then reconnect.)

Since you will eventually have to disconnect the 12V battery anyway to clear the DTC, why not do it upfront if you want to store the car for an extended period. This disconnection is a reasonable alternative to buying a battery minder and leaving it hooked up to the 12V battery - if the 12V battery is fully charged before storage.

Also note item C13 which requires the tech to log the 12V battery state of charge and indicates the minimum SOC is 75%. Perhaps this step was omitted when your car was being prepared for delivery to you.

 

Okay so if I understand correctly, even if I pull the fuse for the dome I will still have to undo the battery connection to reset certain things in the car (radio and clock)? If I don't care about those things being set do I still have to unhook the battery? I guess I'm just trying to figure out the most managable way to do this. I travel for a living and am sometimes only home a day or 2 between jobs so whatever I do I will have to do it often. I love my Prius but I really am struggling with this situation having to jumpstart my car everytime I return. I'm looking for the easiest and safest solution. I did actually try to unhook the battery it's on really tight and when I asked the Toyota guy today to loosen it he said don't bother unhooking it as this circut thing will be just as effective. He didn't mention the fact that I'm gonna have to unhook it anyway, as usual he only had half the details. I downloaded your new doc and will give it a read! Thanks so much for your assistance this whole thing has been driving me nuts.