Auxiliary battery keeps dying

Yes, the amp is always powered from a 30 amp fuse in the engine compartment. A relay would be the simplest and cheapest foolproof solution. The only caveat, is that whatever is causing the extra current draw in the amp will not cause the amp to eventually fail. A suitable relay can be purchased for under $10. You could put it in the fuse holder area, and wire it from the 30 amp fuse contacts, pulling the fuse, and putting the two relay contacts, with a 30 amp fuse inseries between the fuse contacts. You could power the relay coil from the fog fuse, which is switched and ground, and located two fuses below the amp fuse.

 

You have not followed the best advice given so far by MR Wong. A current draw check when the car is off.

It may not be the amp at all. Why bother arguing with the Toy rep when you don't even know if its the problem? You have not done due diligence. Without that current draw check your betting another $200 battery. Not sure what the problem is with you getting that check from the dealer as its pretty easy. And you already said you know a stereo shop.

The dealer probably pulled the 30 amp fuse to the amp. Go look at the fuse box. Its probably now missing as most are to lazy to bend over and look under the seat. Most likely the dealer pulled it just to get you to mozy along and out of there hair.
You may not have fixed the issue. Just working on assumptions.Its probably that but.....

Go to Best Buy. They have some good car guys there. Don't go in the store. Go in there garage on the side. Strike up a conversation with the install guy there. Tell him your issues. Ask him if they have a decent volt/ammeter that can measure quiescent current being drawn from the battery when the car is off with the amp back on.
Tell the guy in addition to the Best Buy fee you'll duke him $20.
if he doesn't f' your car up. Thats always works for me. And him.
Follow Pat's advice. Car off neg side cable off measure in dc amp between the batt and the cable or ground.

If your drawing more than 50mA with the 30 amp car stereo amp fuse removed (like it is now) and the car off than its not the amp and could be anthing. ECU's, damaged wiring, corrosion, collision damage, it goes on and on. Hope it's the amp. Thats easy and cheap. If you replace the amp fuse and its pulling like 1 or 2 amps with the car off..... bingo.

Buy a new power amp there and drive away.

 

With $20+ it may be a better investment to buy a digital multimeter. Just my 2 cents. Good luck!

 

Dave...can you please tell me exactly what the solution was? I am having the same issue. Do I just need to discounted the power to the amp? Can this be done by me? If so...directions would help or do I need something else?

 

Kim needs to consider the possibility that there's nothing wrong with the car other than a close-to-dead 12V battery. It is necessary to measure quiescent current draw when the car is IG-OFF, to determine whether any other problems (like a JBL amplifier not turning off) are present.

 

Thanks for posting this story Dave. I seem to be having a similar problem with my 2006 Prius. About a year and a half ago the battery started dying if the car sat for 2 days. Since I had the car nearly 5 years, I figured it was time to replace the battery. I did this in April and saw no problems all summer. Then come October it started again. I got through the winter with a self jumper and this summer the problem did not occur once. I even left the car for a week and returned from vacation to find the car start up just fine. But here we are in October again, and the problem has returned. This year it seems worse because I drove the car a lot last Friday and it was dead within 24 hours. It had always taken at least 2 days in the past.

 

How many miles is the car driven, per month?

If you don't drive the car much (at least 1K miles per month), you should use a battery charger to fully charge the 12V battery at least once per month.

 

If he has just had his battery replaced, and the same problem re-appeared, how would buying a Yellow-Top solve the problem?

 

A bit of archaeology - but what the hell...

Prius it needs close to nothing to boot all ECUs up (let's say it be 100W (8A) for 10secs). Very short time (if charged with 1A, you will need approximately minute and half) is required to give back that energy back to the battery.

In a Prius there is no starter that is the main energy draw in a more conventional car. Yearly mileage has no effect on the endurance of the battery here.

 

Not true.......as the experience of a LOT of users on here gives testament to.

While mileage itself is not important, sitting unused for long periods of time IS VERY important.
Letting a battery go flat and stay that way very long decreases it's life span.

This has been discussed in great detail in maybe 50 different threads on here already.

 

This statement is incorrect in several respects:

1. The peak current draw will exceed 30A because the brake actuator pump is running. If the owner keeps the cabin heater and headlights turned on at all times then the PTC electric heaters will draw an additional 20A or more while the lights draw another 10A or so.

2. Are you unaware of the quiescent current draw that the Prius imposes on the battery when the car is IG-OFF? This tends to run around 0.02A. Multiply that by 24 hours a day, 7 days a week and pretty soon you will see that lack of use will result in the 12V battery suffering a deep discharge:

0.02A x 24 hours/day x 7 days/week x 3 weeks = 10.1 Ah. Compare to the battery capacity which is ~40 Ah. If the battery started at 100% charge which is a highly generous assumption, now the battery is 25% discharged after three weeks of sitting around. More likely, the battery started at 60% or 75% of full charge so now it is getting dangerously discharged - usually 50% discharge is the lowest a battery should be allowed to reach for good service life.

The DC/DC converter maintains 12V bus voltage at 13.8VDC. At that relatively low voltage it will easily take several hours to recharge the lost 10 Ah.

Some owners think that if they drive the car for 20 minutes, all is well. Those are the owners left scratching their head when the car fails to start and wonder why they are so unlucky.

So if you are the kind of driver who logs 5K miles or less, you definitely need an auxiliary means to keep the 12V battery charged or else don't be surprised when you need to change the battery at 3-4 year intervals.

 

I am having a related issue and hoping you can help me diagnose it. In my case, my wife drives the Prius about 12.5 miles daily (round trip to work being about 6.2) Monday through Friday. What sometimes happens these days is that on a Saturday, after taking the car out for another short trip and leaving it for about two hours, it will not start again. Then when I arrive and jump it, it starts easily. Notably, the clock retains its time and the stereo its presets. I have an Optima yellow top (maybe about two years old). The doors open using the SKS system, but then the ignition won't engage, and I think there are no dashboard indicators at all, but I can't remember. We were just away for four days, and it started upon our return. I suspected the JBL amp, per this thread, so I followed Mr. Wong's advice first. When I tried to use my multimeter (DC ammeter) to check for current, I couldn't get any reading at all. I took it to a local stereo/electric shop, and the tech helped me run diagnostics. The battery had a good charge. We ran lots of electronics with the car off to run it down a bit, and it drained slowly, not anything unusual. Once restarted, it charged right up. The battery showed the usual numbers, around 12V on its own and 13.8 on the charge. Then he ran the ammeter test (showing me that the screw needed to be fully engaged on the body to make the connection), and there was very little draw, about 4mA. We'd turn on the occasional light, and it would climb very slightly, but there was clearly no great draw on the battery. Lastly, we checked the keyfob batteries, but both were good, right at 3V or slightly higher.
We decided that there was nothing more to do without more data, so I'm to check some things if it happens again: Check the battery voltage - is it really low, or is it normal? Do any electronics work? Are there dashboard indicators? If the key is inserted into the dashboard, will the car start?
My questions to the group, meanwhile: If the amplifier isn't properly turning off, would it show on the ammeter test, since the battery is disconnected first? If the draw only continues, not starts, when the car is off, that's not a reliable test.
Does anything else sound suspicious? Anything else I should check, rather than wait for it to fail again?
Thanks!

 

a 12 volt battery reading 12 volts after the car has been off for 8 hours is either n/g, or needs a trickle charge. if it won't hold 12.5 replace it. and charge the new one to 13 volts before installing.

 

There have been some reports of bad Optima's but I don't know the time frame.
Check all 4 (or more) of the main power connections; 2 at the battery and one to the frame in particular.

It sounds to me like you are an excellent candidate for a battery tender; connected at least once a week overnight.
Just your driving patterns might be allowing the battery to S L O W L Y go flat at times.

 

After leaving the car parked for about 40 hours, I checked the battery. It was at 12.13V, started right up.

Where is the 4th main power connection to check?

 

That battery voltage is very low. Fully-charge the 12V battery now, using a 10A charging rate since this is an Optima.

After the surface charge has dissipated, a fully-charged 12V AGM battery should measure 13.0V. If the voltage does not substantially improve from 12.1V, get a new 12V battery.

If you suspect a particular component is causing the current drain, then an obvious troubleshooting technique is to remove power to that component by pulling the associated fuse. Then see if the current drain issue remains or not.

Consult techinfo.toyota.com to obtain an electrical wiring diagram for your model year if you want to get serious about finding the problem.

 

agree with pat. just because car started, doesn't mean it's a healthy battery. if it won't hold 12.5 minimum after charging, i would replace it.