Normal Battery Problem - question

Lead acid batteries are weakened by being fully discharged and destroyed if left dicharged for and length of time. Deep discharge batteries (like the Yellow-Top) are a little more tolerant of being discharged, but are still affected. You should consider getting a new 12v battery and the best choices are the OE battery from Toyota and the Size 51 Optima Yellow Top (which requires an installation kit - $10 from ElearnAid.com).

JeffD

 

Trotting out the hoary old check-the-battery-yourself chestnut:
http://priuschat.com/forums/newbie-forum/73400-weird-stuff-happening-mpgs-dropping-test-battery.html

If you want to use any accessory for more than a couple minutes, leave the car ON ("Ready") in Park and the parking brake set. Then the car will maintain the batteries as usual. Of course the engine will start and run as needed, so be wary if you intend to work under the hood.

 

This is normal behavior for a Prius 12V battery. The Prius batttery is smaller than a normal car battery since it does not have to provide power to a starter motor to turn the engine over. It has an electric motor and HV battery to do this.

So, this battery basically powers up the computers, pulls in the HV relays and provides 12V power to the car accessories. It does not take much to drain this small battery.

So, as you have found out, be careful in the future with leaving lights and other accessories on. If you are going to be doing this it is better to leave the car in the Ready mode and use the HV battery and not the 12V battery. The ICE will come on to charge the HV battery if needed.

 

40 minutes to a dead 12v battery with only dome lights is NOT normal behavior. the battery should be able to supply 20 amp-hours and still start the Prius. Dome lights need 10-12 hours to kill a good battery.

JeffD

 

Adding to the above posts, the Prius does a fairly lackluster job taking care of the 12V battery. The charging system is unsophisticated. On the other hand, the 12V battery doesn't do much, unless you insist on running accessories when the car is powered off.

Because of this, Prius 12V batteries often live for years in a crippled state, without exhibiting any noticeable symptoms. This is why Evan says to not worry, but Jeff says it's not normal. Normal for a Prius 12V battery isn't normal for other cars.

Your 12V battery is on its way out, but it still has some life. Your course of action depends on personal factors. It comes down to cheapness verses uncertainty. My personal approach is to carry a 12V jump box. That way I can extract the full life from a 12V battery, but avoid being stranded by a sudden failure. You can do that, or just replace the battery and be done with it.

Tom

 

Looking at SG II it seems that the 12 V Prius battery, is always being charged with the car in ready mode.

 

Agreed that it is NOT normal behavior.

IIRC, I have left a map light on in my Prius overnight and it didn't kill the OEM 12 volt. I've never had a no-start situation in my Prius and it's never needed a jump.

 

you're still rocking the 06 battery? I had the original in mine and I've left my dome night unknowingly on for maybe 4 hours with no detriment but it didn't give me that warm fuzzy feeling that I was being smart leaving a 5 year old battery in my car. I ended up buying the optima yellow top.

 

You are correct that the 12V battery is always being charged by the HV battery when in Ready mode. If you continue to operate accessories the HV battery will eventually discharge and the ICE will come on to recharge the HV battery. That is what I was referring to. That is also why if you plan to operate accessories for any length of time it is better to leave the car in Ready mode.

 

I'm not. I changed my OEM to an Optima D51 from elearnid a few months ago. My car was bought new in January 06.

 

I've had one with my original 2006 battery. My wife left a map light on, and it completely drained the 12V battery. On the other hand, we don't drive very often. In this case the light had been on for six days. I suspect it went dead long before the end of that period.

Tom

 

The Optima yellow top battery is a better quality battery than the stock one, and it costs about the same. I've seen posts indicating you can get the Optima from NAPA for perhaps less, but you would still need to get the kit from e-Learnaid. The kit includes a new negative cable and battery termmial and a new positive terminal as the Optima uses "standard" size battery posts, not the smaller ones the Prius stock battery uses. The kit also includes a battery venting kit, so you can route the Optima vent hole to the Prius vent tube.

Ask around at local Toyota dealers about what they charge for a new battery.
The Optima is available from Toyota Prius 12 Volt Auxiliary Battery with install kit for 2004 - 10 and pricing is there.
You could also check with a local NAPA store. I think they call it "N9951YEL" if I copied it down correctly.

 

The best and cheapest bet is to carry a 7amphr sealed battery (alarm) and make up a set of jumpers. Cost: $20.00 ( for emergency use )

 

I want to explain why the battery you choose should be a vented AGM battery.

Toyota put the 12 volt battery in the passenger compartment with your loved ones. Should there be a loss of physical integrity, battery acid could be sprayed about the cabin. AGM Batteries have little to no free acid as a liquid, it is Absorbed in a Glass Mat to reduce any risk.

In some modes of overcharging (which Toyota may have gone overboard to avoid) any Lead Acid battery produce Hydrogen gas which is explosive, colorless and odorless. Hydrogen - Wikipedia, the free encyclopedia As such, you need a vented battery to protect the occupants of the car.

Neither of these events will happen often, but you do not want them happening even once..

So far, in the US, these two batteries seem to be the only safe choices. I am told that in other countries, Optima sells vented AGM batteries that fit with no modification.