Tryed to start my 98 C5 and 7 month old battery was totally dead. I pulled the battery and under warranty so the parts place changed it out and I cleaned all the terminals and put it in and it cranked right up, Tonite I dropped off my daughter and when I got back home and turned off the lights I heard a humming sound coming from I think behind the steering wheel and dash area, I went around the car and the hum was loudest on the drivers side. I checked everything under the hood but the noise was not there only on the drivers side. I think this is what killed my battery I just never noticed it before this morning. Any idea's? I am going to unhook the battery cables so it doesn't kill this battery to so I am in hopes that someone else out there has had the same problem and can steer me in the right direction. We have had a lot of rain this past 3 weeks so its possible that something got wet as I did notice a few days ago that the seat=CD- and other electrical ghost appeared and them disappeared. Aloha

 

I included some of the normal culprits at the end of this post I made a while ago. The BOSE amplifier is probably the issue. If not, BCs advice shows how to track down a drain.

Identifying Battery Problems
The C5 eats batteries unless you take some regular precautions. If your battery continually dies its either the battery which is on its last legs or something on the car.

You also need to look at how you use the car. Is it a daily driver? If so the battery should be getting a good top up every day so you may have a problem.


Is it a DD but you do short trips? If so you'll be taking a lot out of the battery every time you start. For a short trip, say less than about 20 mins, you won’t top it off properly. Eventually it'll drain.

Is it a weekend car. If so, this takes a lot out of your battery. There’s a 20MA drain even dormant. If you don’t drive the car for a reasonable time every week or so, it'll kill the battery. In this case you really do need a battery tender.

You’ll know when your battery is bad. As it gets low you may get strange electrical indications (random warnings and U fault codes). As it gets lower it may drop the memory settings or defaults such as HUD settings. Eventually you’ll get the dreaded chattering relays in the footwell and eventually the lights on the IPC will disappear.

Most batteries can be recharged quite successfully, although AGMs are harder. Start by checking the charge on the battery. Don’t read the DIC when the car is off. The value you see on the DIC is alternator output when the car is running. It will always measure an inaccurately low voltage on the battery when the ignition is off and figures of 11.0V to 11.9V is normal in this case. With the engine on, the voltmeter should show between 13V and 14.5V. You need to measure voltage across the battery terminals using a digital multi meter if possible. A fully charged battery measures 12.7V and a fully discharged battery measures 11.9V. Partially discharged batteries will give a reading somewhere in between.

If the battery is low give it an overnight charge (or put it on a battery tender until you get a fully charged indication) and retest it. A true test is under load and Autozone will do that test for free.
If you have an AGM battery like the Red Top and it has been deeply discharged it's harder to recover it. This might help:
http://www.youtube.com/watch?v=dIoaL3DWWEg

If you’ve recharged it and it still runs down, then you need to start looking for excessive drains. Bill Curlee posted a good method for checking:

http://forums.corvetteforum.com/1567522286-post590.html

There are some common faults which are well known for causing problems:

First to check is the interior lighting rotary switch on the drivers panel. It’s possible for that to be turned on as there’s a setting (fully clockwise) which bypasses the auto off function. Turn it fully counter clockwise and check after about 30 minutes (preferably in the dark) that the interior lights have gone off.

If it’s not the lights something has failed or is badly installed.

Have you fitted an after-market device which draws current? Typically it’s a cellphone charger, radar warner or a similar device that’s the problem.

If still no joy, you need to start pulling fuses to identify the problem.

The power seat switches on the side of both seats are notoriously unreliable. The switch becomes sticky with use and can stick in the “on” position. You shouldn’t damage the motors as they are thermally protected. The fuse may blow so worth checking (Fuse 36 20A in footwell).

The driver’s lumbar motor can also cause issues so check this too (mini fuse 3 15A in footwell). The seat controls connect under the seat. Pull the connector and if the drain stops that’s your problem.

Less common but not unheard of are failures of the headlight motor control module the alternator and the Bose Amplifier under the dash on the driver’s side.

 

Here ya go. The BOSE Amp is #15 behind the kick panel. Id check the connections and clean them up as a starter. Its only held in by a couple of bolts so its easy to change out if it's failed.

 

Thanks I will keep this info in my C5 file but my hearing plays tricks on me due to spending to much time on a firebase with incoming and outgoing, my daughter informed me that the noise or humming was coming from the drivers seat not the dash. as soon as I pulled the seat connector the hum went away. It was wet and the contacts needed cleaning which I did and solved the problem. I changed the motor in the drivers window (thanks forum and youtube) but I think it need adjusting for a better seal as the carpet was wet next to the seat where the connector is. I will do that in the am. thanks again

 

Water on the carpet at those two seat connectors can wreak havoc on the car's systems as the serial interface wire is there along with the telescoping steering column controls and so on.