After being out of town for a week on business, I returned to a dead battery. This has happened twice now ... any ideas of why this is happening? I know our car uses a smaller battery, but this doesn't seem normal. I do have a "battery tender", but I wouldn't think I would have to use it on a car that sits for only a week.
The car is only about 6 months old.
Any help/ideas would be appreciated.

 

I don't think that's normal. I've routinely left my car for one to two weeks at a time and it's always fired up immediately. Do you have an after-market alarm or anything else that may run with the ignition off? Could an interior light be on?

Have the dealer check it out; if they don't find anything else, ask for a new battery.

 

Do you have a big stereo in the car?

 

I do have a BOOMERANG antitieft system and it would drain my battery about every 3 weeks if I don't use the car for that long... Mine is now 2 year old and I just got HONDA to change my battery since it would no longer take charge...

BTW car has only 5 k miles on it.

 

I wouldn't say big ... I have a sony head unit and PG 4ch Amp (400.4). I checked to see if the amp stays on after the car if turned off, and it appears not to be on (lights off).

 

If you have a voltmeter, do a quick check on your battery/alternator.

With the car off the voltage across the battery should be around 12.8V.

With the car on the voltage across the battery should be around 14.2V.

If the voltage is below 14.2V when the car is running, you may have an alternator problem and it is not recharging the battery.

BTW, never disconnect a battery lead with the car running. A quick way to fry the electronics in the car.

 

[QUOTE]Originally posted by matrix
[B]If you have a voltmeter, do a quick check on your battery/alternator.

With the car off the voltage across the battery should be around 12.8V.

With the car on the voltage across the battery should be around 14.2V.

If the voltage is below 14.2V when the car is running, you may have an alternator problem and it is not recharging the battery.

BTW, never disconnect a battery lead with the car running.

 

Depending on the current draw current draw of your stereo (and everything else running the car), the alternator may not be able to keep up, thus the battery will provide whatever current is required beyond what the alternator is providing and be constantly draining.

If you have a large system, it may draw more current than what the alternator can provide, particularily if you play it loud for long periods of time. Over time the battery will charge and discharge normally but will wear the alternator as it was not designed to constantly recharge the battery.

Okay, so you have a 400 x 4 so I am going to assume that means 100W RMS x 4. RMS stands for Root-Mean-Square. A peak ac signal (the music) is put through that mathematical calculation (Root-Mean-Square) to find the equivalent DC current of an AC flow. So in your case, you have a 100 W RMS amplifier...that means that the amplifier will provide about 141 W per channel of peak power (to find this number divide the RMS value by .707). 141 W x 4 channels = 564 W of power that your amplifier is requiring.

So if your car's electrical system is okay, the output voltage of the alternator is about 14.2V. To calculate how much current you need to provide use P=E (Voltage)*I(Current).

We know E = 14.2
We know P=564
Solving for I we get about 40 amps.

So your stereo will require about 40 amps to run. In your case, your stereo should be okay, but it will depend on what else the alternator is running ie the lights, etc.... If it is constantly charging the battery, the draw on the alternator will be high.

This assumes you are running a 4 ohm load (speakers), if you are running a lower load the power output of the amplifier will be higher and since the voltage source cannot provide more voltage the current will go up.

Hope this helps...

 

[QUOTE]Originally posted by matrix
[B]Depending on the current draw current draw of your stereo (and everything else running the car), the alternator may not be able to keep up, thus the battery will provide whatever current is required beyond what the alternator is providing and be constantly draining.