I have a friend with a 99 who is now on her second battery in the car. The first one died completely and the second is now going (only 7 months old - installed by a Chevy dealer). She leaves the car sit for more than 12 hours and it's a bear to start. I had a similar problem with my 97, but after all my battery was 4 years old. Replaced it and have had no problems since. Well, she keeps going to the dealer and they can't seem to find anything. I vaguely remember a post on the forum regarding the alernators on the C5's. Is there a service bulletin to have the alternator checked? Is anyone else having this problem? :confused:

 

I have NEVER been anyplace, includeing back yard mechanics who don't check the alternator output etc when replacing a battery. If that dealer isn't checking alt. output etc., she needs to find a new dealer. ;)

 

I agree with rocknrod...Get another dealer....There is either a big drain on the battery when shut down and/or the alternator isn't up to par...Of course if the battery is being run down, you ask the alternator to work extra hard when you do run the engine.

 

I think everyone is on the right track in suspecting the alternator. I think that current may be bleeding back through the alternator possibly because of a bad diode.

Next time the car is going to be setting for a while, you can unhook the Batt wire to the alternator (tape it so it can't accidently ground and cause a fire) and see if the battery still runs down. If it does then my guess about a bad diode is wrong.

Good luck.
Mark


[Modified by MDT, 12:34 PM 8/4/2001]

 

Something else to consider: Are there any "aftermarket" devices installed on the car, i.e. alarms, radios/amplifiers, "hardwired" radar detectors? If so you might want to consider disconnecting it/them to see what happens. If problem goes away then check where the power source for these devices are hooked into car's electrical system. These devices should only have power when the key is on.

 

I was sure my AGM battery on the 2001 Coupe was going South and had the
dealer check. They said nothing was wrong with my batter but found a weak
sister alternator. They replaced it and I have not had any battery problems.

dick

 

The standard 105 amp GM alternator is a POS. It has a partial failure mode that fools most mechanics into thinking you have a battery problem. It even fools most of the new automatic battery/alternator diagnostic testers that the techs use. I just put my 3rd alternator in my C2500 with 45k miles. I had to argue many times with the techs who tested my truck and said it was my battery.
The failure mode is that the alternator cannot put out full amperage anymore. It will put out > 13 volts though, fooling you into thinking it is OK. The engine, accessories and DRL's in most GM cars draw a ton of current. If the alternator is only putting out say 50 amps, then it starves some of the systems or the battery for power. The car will run and start, but over time the battery will go dead and some sytems will operate irratic.

The only real way to test the charging system is to use a DVM and a DC clamp on current probe. Measure the total amperage coming out of the alternator and then see how it splits between the various systems and the battery. A bad alternator will put out say 40 to 60 amps and only 2 to 5 amps will be left over to charge the battery. You also need to measure voltage drops across wires to make sure you don't have a bad terminal on a cable or a bad ground.

If your battery has ever gone dead, you jump the car, and then run it without fully charging the battery, your alternator will overheat and have a shortened life. The alternator also will have a shortened life if you use the AC and lights a lot. An large aftermarket stereo will also overheat the alternator.

 

99HT,

Good post. The 42 volt systems are due out in 2004, last I heard. We really are in need of something more than a 12 volt system.

Later.
Mark

 

Have them check the voltage drop across the battery cable at the full load of 100 amps with a good digital multi-meter. The 7ft long cable is undersized and creates an unwanted voltage drop, thus starving the battery. The drop should not be more than a few 10s of millivolts. This cable could also have bad connections. A co-worker replaced his with a 2 ga wire and his battery charging problems disappeared.

Bob

 

I still have my original alternator and Delco battery and so far no problems. I recently added a 250Watt (RMS) amp. with a 10" Sub-Woofer in the trunk. Still no problems. He could possibly have an alternator problem, but I would still like to know if there are any add-on accessories that are'nt installed properly too. Ya just never know!


[Modified by Tx99FRC, 7:49 PM 8/4/2001]

 

There is a known problem with the glove box switch. Go out at night and look at your glove box when it is closed. If you see light around the edges, your glove box light is always on. The C5 does not control the glove box light like say the mirror lights. It shuts down most lights if they have been on for more than a certain time.

I had to put a self adhering rubber foot on my glove box door to assure the light switch is fully pressed.