[DevilleNut]

Guys,

On Wednesday, we drove the car and parked it in the garage. My wife went out tonight to open the trunk and found that none of the interior lights turned on so it looked like the battery was completely dead. However, I did not check the battery voltage with a voltmeter to see what it actually was. I connected my 10 amp battery charger and turned it on. The battery started charging at about 12 amps (on the meter). After about an hour and a half, I disconnected the charger and checked to see if the lights worked, and they did. When I reconnected the charger, it continued at about 12 amps.

Any ideas on what could have discharged the battery after only two days? It's only 2 years and 9 months old, but I guess it could still be defective. I have a Schumacher digital battery tester that I can try when the battery is fully charged, but it looks like that will be quite some time...maybe tomorrow at this rate. In order to use the tester, I have to input the specified Cold Cranking Amps. Since the battery is under the back seat and my back muscles are currently incapable of doing any work does anyone know what the CCA rating of a Delco battery for this car is supposed to be?

 

[Byrdman]

First and always, did you pull codes to see what might have caused the problem?

 

[DevilleNut]

First and always, did you pull codes to see what might have caused the problem?

Not yet. I wanted to wait until the battery was recharged rather than turning things on with the charger connected. I'll let it charge over night and then check it in the morning. I can have a shot at using the Schumacher tester then, too, but I'll have to guess at what the CCA rating might be.

I also have a Harbor Freight battery load tester which loads the battery for 10 seconds at a high current. Is there any problem with connecting this to the charging point under the hood? I'm not sure what gauge wire is used from that point to the battery. I don't want to burn something out which would be infinitely worse than just needlessly buying a new battery.

 

[DevilleNut]

I may have found the problem, but I'm not sure I completely understand it. When I went out this morning, I found that the charger was still pumping 5 amps into the battery. I disconnected it and then went into the car to pull any codes. I happened to notice that the shift indicator display was illuminated the way it is when the ignition switch is set to the Accessories position. There was no key in the switch. For some reason, when the switch was supposed to be off when the key was removed, it was still in the Accessories position. I should have checked to see if the windows worked, which would have been a sure indicator. I turned the switch to the Off position and the shift indicator went off. I'm guessing that the ignition switch was in the Accessories state for two days and I can see where this would have drained the battery.

I did pull codes and there were dozens of them. Almost every module in the first half of the code scan had at least one code. I'm guessing this was due to the battery going flat with the ignition switch in the Accessories position.

I connected the battery tester to the charging point under the hood and ran the Battery test, and when it did the CCA test, it indicated BAD. Part of the test is based upon inputing the CCA rating of the battery which I don't know. I just guessed at 750 amps. There is a lot of wire between the battery and the charging point, so that may have contributed to failure indication also. I'm going to take the car to a shop on Monday and have them test the battery at the battery terminals to see it's actual state.

 

[Submariner409]

Cadillac wants at least 800 CCA for the Group 79 vented battery under the back seat.

A dead cell will kill a battery overnight - NOT uncommon. - battery age makes no difference.

A dead/nearly dead battery will accept a pretty high charge amperage until it nears full charge; internal resistance then signals the charger to ramp down the charge rate, both voltage and amperage. At full charge a good smart charger will produce literally NO amperage and will hold the battery at 13.1 - 13.3 volts.

A fully charged battery, disconnected from anything for a half hour should read 12.6 volts.

EDIT: Saw your latest post. Yes, the highly unlikely switch in ACC would kill the battery quickly as well as set a slew of U-codes. (U = Power and data)

 

[DevilleNut]

Sub,

Thanks. This may have been a combination of a weak battery and the ACC switch being on. Maybe I'll go out later and read out some of those U codes and see if they are related to power. If the ACC switch was on while the battery was being charged, this might explain why the charger was still inputting 5 amps after about 20 hours of being on the charger. If that's the case, then if the car was using 5 amps through accessory power, that would leave only 5 amps to go into the battery to recharge it.

 

[Submariner409]

U codes are ALL related to power and data glitches. Entirely possible, due to power loss, to see a XXX no communication or no data.

With the ignition switch in ACC or ON the car draws 3 to 6 amps, depending. If all's normal the parasitic draw should be about 15 - 20 mA but you have to jump through many time and power cable hoops to accurately measure that. One of our cars will kill the battery in 3 weeks to a month of storage.

Good idea to use a Battery Minder. My garage queen STS sits there, Battery minder plugged in, never a battery problem - and a Battery Minder greatly extends battery life if used regularly. It DOES NOT need to be any larger than 0.5 - 1 Amp capacity - it's NOT a charger - it keeps a good battery charged.

amazon automotive battery minder - Google Search

 

[DevilleNut]

Sub,

I knew that the U codes were related to data glitches, but did not realize that they also related to power problems until you mentioned it.

Our Cadillac never sits idle for more than a couple of days a week so I don't think that I need a battery minder for it, but it might be a good idea for our Falcon that sits unused all winter.

 

[Submariner409]

Our cars also have RAP - Retained Accessory Power - that keeps some accessories hot for 10 minutes after Key: OFF. Sometimes one of the accessories stays hot and that drains the battery. Do you have anything plugged into one of the 12V power ports? They can be configured to turn off with RAP or stay hot at all times, so a phone or charger will kill the battery in that case.

The power port fuses in the underhood fuse box have two possible positions - RAP or always hot.

Here's my setup - yours may differ slightly. Use the locator legend inside the fuse box top.

 

[DevilleNut]

Sub,

Thanks for the info. I have my fuses configured so that the cigar lighter socket is on all the time and the power socket in the front passenger's seat is hot when the accessories are on. I have a little USB charger plugged into the cigar lighter socket, but the only time it gets used is once or twice a week to recharge my wife's flip phone. The rest of the time, it only has a tiny red LED drawing power. The power socket in the seat has the backup camera plugged into it so it only has power when the accessories are on. This configurable power design is great and somebody at Cadillac had a good idea when they designed it.

 

[Submariner409]

That USB charger may have a small transformer to drop the 12.6 - 14 system voltage to 5 or 6 volts for phone charging. It may be a bit more of a constant drain than you think.