battery constantly dying

Replacement after that many years is normal. 12-Volt batteries only last so long, especially when you have SKS and an alarm.

Having the new one die could be anything. How long did it sit? Could it have been just a fluke leave the lights on or a door ajar error? Has it failed since? Of course, it could just be a bad replacement too.

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Driving once a week would be enough, if you keep the car READY for at least 30 minutes. Once a week is not enough if you are only driving 2 miles.

 

Can you give a better explanation of why you need to run for 30 minutes or more? Is it due to a slow trickle charge from the inverter? What it going on?

 

The inverter is a slow charger of the 12v battery. It generates about 14 volts to provide charging current without overcharging the battery if you are doing a long trip. If you drive intermittently for short drives, consider buying a "battery minder" and use it to maintain your 12v battery at full charge when not in use.

Note that you can get a better battery for your Prius than the one from Toyota at:
http://www.elearnaid.com/12vo1topraub.html

JeffD

 

The search tool is a wonderful thing ... tons of posts on the battery, AND the best replacement (NOT oem) that eliminates the quick drain issue.

 

Sorry to hear of your 12v battery problems. It appears to be one of the few weak points in the Prius engineering. My elderly parents, who drive their 2007 Prius on very short trips a few times a week, have had the same problem--see this thread which includes a summary of some of the most helpful threads:

http://priuschat.com/forums/care-ma...07-12v-battery-dies-4th-time-please-help.html

Following the good advice of several Priuschat members, my parents now have one of my brothers drive their Prius for at least 20 minutes at a time, at least once a week, and they have not had the 12v battery go dead since.

My 2007 Prius, on the other hand, has not had any problem whatsoever, but we drive it daily to work & back, usually around 20 minutes each direction.

Bill N., Ypsilanti MI

 

+1. The Prius just hates to be driven less than 10 minutes. If you do this, it will start to have problems.

 

Make sure you didn't accidently hit one of the little light switches in the rear hatch area. It's very easy to have one of those lights stay on and not notice.

 

Since this topic comes up repeatedly, does anyone have a method for reading the current draw of the vehicle when it is sitting with ignition off? Seems that what is really needed is a way to quantify the drain and compare it to vehicles without the problem. That way readers could quickly sort out whether or not the battery was at fault, or something else.

 

Yes, that's fairly easy. Clamp a DC ammeter around the plus lead of the battery.

As for sorting it out, it's almost always the battery, unless a light is left on. When you leave something on, an ammeter isn't going to help, since you won't test it every time you shut down.

Tom

 

Hi Shawn,

The exact current draw will depend upon whether the vehicle has Smart Key or not; and also depends upon whether aftermarket accessories (i.e., alarm system) are installed.

The method of reading current draw is to use the ammeter function of a digital multimeter. However one must keep in mind the maximum current that the multimeter can handle, and ensure this is not exceeded.

For example, I have two Fluke meters, and one has a 10A limit while the other has a 2A limit. If I were to try to make the car READY while the meter was in the circuit, either meter's fuse would blow (since peak startup current draw is around 30A).

At an earlier time when I was interested in this subject, I measured the IG-OFF current draw on my 2001 and it was around 30 mA. I think that 2G will be at a similar level.

For discussion, suppose that 30 mA is a good number for 2G IG-OFF current draw. Also suppose that the 2G was left in an airport parking lot for three weeks.

.03A x 24 hours/day x 21 days = 15.1 AH.

The 2G battery AH rating is somewhere in the low 30s, and it normally is considered acceptable to drain the battery to 50% or so. Hence, a 2G with a battery that is in excellent condition should withstand storage for 3 weeks without a problem.

However, if the battery is not fully charged prior to vehicle storage, or if the battery has marginal capacity, then it will discharge to the point where the car refuses to start.

 

Ouch, those heavy clamp on DC meters aren't cheap! So much for the direct method. Electrical engineering is not my strong suit.

If one could get a baseline, then it would indicate if something was draining the battery (after subsequent drain and recharge.) So if the problem appeared, one could hook up the meter after the battery was recharged, then read the current drain periodically. (Would be best if it could also pick up peak drains in case something was turning on intermittently.)

No, it won't help if it is a light left on, but it will help for faults in the system. I've had shorts before that drained batteries and were difficult to detect. I'm pretty sure a dying ignition switch has done this to me on the Accord (wasn't apparent until the switch finally died), I had similar intermittent shorts on an ancient AMC, and I suspect a bad dome light nipped me on the Tundra.

This latter one with the Tundra was odd because the bulb was not functioning, but was not physically burned out either. I think the switch had gotten turned to the on position by the kids, but with a dead bulb I didn't realize it. I wasn't driving the truck much for awhile and it was cold so it is a toss up as to what started giving me battery trouble. I thought at first I just needed a fuse, but when that didn't work and the bulb looked fine I checked the voltage across the contacts and realized I must have a bad bulb. A replacement bulb did the trick for the light...but I still don't know if the battery drain was related or coincidence.

 

Thanks, that is the sort of test I had in mind. I've had an old digital multimeter for a long time but the 10A limit on it has prevented me from ever really trying it for current for the reasons you mention.

One can always dream of a simple, inexpensive inline or clamp on device to read the current, to log data, and show peak loads.

 

Are there any aftermarket electronics or mods?