Car Stereos: After Market Radio Memory Loss, dead cells, market radio

Question
Mark:  I've been told by the professional installers at the radio shop that the reason my Sony stereo keeps losing the stations I've set and returning to Demo Mode is due to the fact that their are "multiple dead cells in my battery and that my stereo is not receiving sufficient power to retain it's memory."  I think this is a crock, the mechanics at the Ford dealership have never heard of such a thing and confirmed there is nothing wrong w/ my battery and in fact it starts my car each and every day and all the computerized items in the car work fine; and yet the radio can't function properly.  What do you think?

Answer
Hi Tammi,

I'm skeptical of the installers' story as well, especially if the battery has been tested and no problem found.  "Multiple dead cells" should be very obvious in a battery load test.  

Generally, if you have dead cells in a battery, this could result in excessive voltage drop when you start the car--the problem will be most severe when there's a heavy load on the battery, and operating the starter is the heaviest load you'll find.  So, one test would be to turn the key to "accessory", and play the radio for a moment, before you start the car.  Store a station preset, then turn the key off.  Wait at least a minute, then turn the key to "accessory" again and see if the station setting was lost.  

If the station setting wasn't lost while the car was turned off, then start the engine and check again.  If the setting is lost after the engine is started, that might indicate a battery problem--the voltage may be dropping so low during the engine cranking that it erases the radio memory.  On the other hand, if the station setting was lost during the minute that the car was turned off, it's not going to be a battery problem, because a bad cell shouldn't affect the radio when there's no significant load on the battery.

The more likely cause is that the radio's constant and accessory power wires are connected improperly.  If the wire connections are reversed, then the radio's constant power wire will lose voltage whenever the key is turned off, and the memory settings won't be retained.

The only problem with this theory is that no professional installer should have overlooked it.  This is such a common problem, and so easy to test, that it's hard for me to imagine any remotely competent installer blaming the battery instead of a simple wiring error.  

The test is simple, if you have a voltmeter handy and can get to the wiring at the back of the radio.  The head unit's constant power wire should be yellow.  Just test the yellow wire to see if there's voltage present when the key is switched off.  If there's no voltage, check the red wire--this is the accessory (key-switched) power wire.  If there's voltage on the red wire, but not on the yellow wire, with the key off, then just reverse the two connections; this should solve the problem.

Hope this helps!

Brian