Help with dead car battery

[Grant Wilkinson]

What is the make and model of your car? You may find on a forum about that car that there is a known frequent failure that draws power. On my car, for example, it's a known that the hands free Bluetooth module fails and will kill a battery over night.

[Brian Henderson]

thanks I'll try this as Im not good with meters I have a voltage meter but not sure what they mean by meter in series with battery?

If you have a battery charger, they almost always include a rudimentary meter on them.

[Jim Koepke]

A good charge on a batter should give a voltage reading in the 13V range with the car not running. When the car is running and the alternator is charging a volt meter will read in the 14V range.

Watch the meter when the car is turned off. The reading should be fairly steady. If it is dropping something is draining the battery.

In the old days we used to just disconnect the cable while in the shade and touch the cable to the battery terminal and watch for a spark. The bigger the load, the bigger the spark. That doesn't work well with todays system because some will draw a large current when reconnected, causing a larger spark.

A decent amp meter is a better way to monitor battery drain with the system turned off. As mentioned previously, removing one fuse at a time can help isolate what is causing the drain on the battery if it isn't a bad battery or charging system.

Beyond this, trying to explain how to measure electrical circuits and explain the problems that can ensue could take a lot of time and effort.

jtk

[Bert Kemp]

Thanks for the replies, its been pouring rain all day so have no had a chance to try any of these things hope tomorrow is better, I'll let ya knoow

[Brady Watson]

FYI - Don't just go buy another one without realizing that the one you have most likely has a pro-rated warranty...If it has a 5yr warranty, you'll only pay 1yr worth of use.

Some batteries, regardless of how new they are 'go bad' because one of the cells shorted out etc. I stopped buying Optima batteries @ $140-200 ea because I got 2 bad ones in the same year. Previous ones lasted 8 years...

To save your sanity ~ and to buy you time to diagnose the issue, here's what I'd do - I would get a new battery and a post-top battery disconnect switch. This can function as an anti-theft device later...but it will let you save the charge on your new battery should you determine that there is a short happening somewhere without the need to pull cables every night and give you piece of mind if you want to take your favorite girl out to the movies or something without worry.

In terms of diagnosis...my path would be to print out a fuse box schematic & start probing circuits with the ignition key out/off and see if you're drawing power from anything that shouldn't be on. Naturally you'll get a hit on the courtesy/dome lights, but you shouldn't have a draw at too many other places. Check the schematic to see where you get a hit and that should point to the problem.

Look on Amazon etc for "battery terminal switch"

Good luck!

[Paul F Franklin]

Be aware that with many newer cars, disconnecting the battery without using a memory saver or similar device can erase radio settings, saved seat settings, phone pairing data, and the like. Maybe not a big deal, but my wife probably has 30 or 40 radio presets on her car between AM/FM and satellite......She would not be happy if she had to redo them all.

[Bert Kemp]

FYI - Don't just go buy another one without realizing that the one you have most likely has a pro-rated warranty...If it has a 5yr warranty, you'll only pay 1yr worth of use.

Some batteries, regardless of how new they are 'go bad' because one of the cells shorted out etc. I stopped buying Optima batteries @ $140-200 ea because I got 2 bad ones in the same year. Previous ones lasted 8 years...

To save your sanity ~ and to buy you time to diagnose the issue, here's what I'd do - I would get a new battery and a post-top battery disconnect switch. This can function as an anti-theft device later...but it will let you save the charge on your new battery should you determine that there is a short happening somewhere without the need to pull cables every night and give you piece of mind if you want to take your favorite girl out to the movies or something without worry.

In terms of diagnosis...my path would be to print out a fuse box schematic & start probing circuits with the ignition key out/off and see if you're drawing power from anything that shouldn't be on. Naturally you'll get a hit on the courtesy/dome lights, but you shouldn't have a draw at too many other places. Check the schematic to see where you get a hit and that should point to the problem.

Look on Amazon etc for "battery terminal switch"

Good luck!

Never heard of that but will definitely get one it will save my sanity for sure , but maybe wait till after takin my girl out if ya know what I mean LOL

[Brian Henderson]

Be aware that with many newer cars, disconnecting the battery without using a memory saver or similar device can erase radio settings, saved seat settings, phone pairing data, and the like. Maybe not a big deal, but my wife probably has 30 or 40 radio presets on her car between AM/FM and satellite......She would not be happy if she had to redo them all.

Most new cars have a backup battery that saves all of those things for at least a short while. Otherwise, you could never change a bad battery!

[Jim Koepke]

Most new cars have a backup battery that saves all of those things for at least a short while. Otherwise, you could never change a bad battery!

When a technician changes a batterie in a shop they often connect a 12V power supply to the car, change the battery and nothing is lost. A person could likely also use a battery charger. Be careful with the positive battery cable if you do this. If it hits ground you will wish had paid attention.

In my car, it all just gets reset as needed after disconnecting the battery or replacing the battery.

jtk

[Bill Orbine]

Be aware that with many newer cars, disconnecting the battery without using a memory saver or similar device can erase radio settings, saved seat settings, phone pairing data, and the like. Maybe not a big deal, but my wife probably has 30 or 40 radio presets on her car between AM/FM and satellite......She would not be happy if she had to redo them all.

Are you concerned with that when the battery already has been dead?

[Jason Roehl]

Are you concerned with that when the battery already has been dead?

There are different degrees of "dead" when it comes to car batteries. The first is that it won't start because that requires a HUGE amount of energy from the battery. Such a battery that is just below the charge threshold needed to start a car can easily power the radio, interior lights, even run power windows, but those things start dropping off as well. Way down on the list of power requirements are memory settings in the chassis computer (seats, pedals, etc.) and the radio presets, as internally those electronics probably only need about 5V. A 12V car battery is a nominal voltage (in name only)--if your battery reads 12.0V, it probably won't start. A bare minimum would be about 12.5-12.6V in my experience, and a new, fully-charged battery can be over 13V, all of this with the car not running. With it running, a working alternator will show 13.5-14.5V on the battery.

[Grant Wilkinson]

A bit off topic, but I worked in a shop that replaced batteries daily. We had a device that you can find online that plugged into the accessory socket (used to be the cigarette lighter socket). The device contained a 9 volt battery and with that plugged in, you could disconnect the car battery without killing any of the electronic presets like seat positions, radio presets, etc. The units are pretty cheap and handy to have around.

[Bert Kemp]

Not worried about losing settings or anything like that. All I want to know is if theres an abnormal draw on the battery when the car is off or if the battery is bad. I put the charger on it early this morning will let it charge till the charger shuts off. I will then let it sit over night disconnected and see what it read in the morning. Or maybe be3 bold and take it to auto shop and have them check it .My problem with that is they can always say its bad just to sell me a new battery and those places always have high priced battery's

[Brian Henderson]

When a technician changes a batterie in a shop they often connect a 12V power supply to the car, change the battery and nothing is lost. A person could likely also use a battery charger. Be careful with the positive battery cable if you do this. If it hits ground you will wish had paid attention.

In my car, it all just gets reset as needed after disconnecting the battery or replacing the battery.

jtk

Whereas mine, which was just in for work, didn't. I got it back with all of the settings retained. I guess it depends on the car.

[John K Jordan]

Whereas mine, which was just in for work, didn't [use an aux 12v ps]. I got it back with all of the settings retained. I guess it depends on the car.

A simple addition of an appropriate capacitor to a DC circuit can supply low current levels for a significant time to hold settings. Perhaps some of the car makers do this. Also, non-volatile memory is so cheap now that they could easily use it to preserve settings in today's computer-controlled cars.

Tidbit: In the '80s I had a small "super capacitor" that would run a small 5-volt DC motor for maybe 10 minutes. Very expensive then.

JKJ