Cadillac Repair: Cadillac Deville 1989 Front Wheel Drive, h stern, ampmeter

Question
Have had two new batteries installed within the last 4 weeks.   Original complaint was battery dead or weak and would not start car.  Sears installed new battery and checked alternator etc.   When car was not in use for several days battery would not start car.  Jumped start and worked fine but would not start again after stopping.  Sears checked again found nothing wrong installed new battery.  Now have same problem  Alternator checks fine.  What is the problem.  Can find no visable signs of lights, radio etc. being on after ignition turned off.  Battery and alternator cables where checked.  There is a drainage of electricity from the battery when car not in use or there is a device between alternator and battery not functining.  How can this be determined.  

Answer
Hi H.Stern, You are probably correct that something is staying on and causing the battery to drain. Lets start with the battery first. If you put the minumum size in which is 540cca that could be part of the problem. Because you don't drive your car everyday and your computor systems keep a constant drain on it I would recommend useing a battery no smaller than 770cca. I had my dad install a 1000cca battery in his '91 Deville because it was the same price as the 770cca and was a Delco to boot. Now how to locate the draw? First off check for the obvious lights being feft on. At night open the trunk just a crack to see if the light is on. Do the same for the hood light and glovebox light. The interrior lights will be obvious if they are on. Now comes the harder part. What you need it a digital ampmeter capable of reading from 5mA(milliamps) or .005 amps up to 20 amps. The reason being is that under testing conditions you might have 10amps being used from the battery and that would blow the fuse in the smaller 10amp meters. I am not aware of a clamp on meter that reads to 5mA but maybe one is available  cheaply in which case you will not need the battery switch. Then you get a disconnect switch that goes between the battery cable and the battery. With the switch closed you need one lead of the meter on one side of the switch and the other meter lead on the other side so when you open the switch all current flows through the meter. The neg lead needs to go closest to the negative side of the battery and the pos lead then goes closest to the pos battery side. With the switch closed start the car and run it for 5 minuits with all the acessories on that you normally use. Then shut off the key and remove it, open the drivers door and close it and then open the switch on the battery cable and read the meter. If there isn't a draw your meter should read less than 15 mA or .015A after 20 minuits. If after 30 minuits you still have a higher draw then you will need the start unplugging fuses and removeing fuse links untile the reading drops to less than 15mA. Then it is a matter of unplugging things on that circuit until the draw again drops and that is the part that needs to be replaced. Don't forget to unplug the alt connector as it can test good but still cause a draw. I have also found the height sensor to cause a draw. When you start to pull fuses make sure the first on that is pulled is the body or ctsy fuse so the interrior lights turn off and leave it out. Then one at a time remove a fuse, watch the meter and if no change put it back in and go to the next fuse. With any draw it might take several tries to get the draw to happen over the course of several days. Always remember to close the battery switch before starting the engine or your meter might get damaged or at the very least you will need to replace the fuse. Hope this makes sence and if you need more help repost and I'll try to help. Happy hunting. Bill