My 1995 E420 appears to have the original battery and I want to replace it soon. I think I will have to re-enter the radio code once the new battery is in. Will there be any other codes needed if I don't maintain power to the car while the battery change is being made? Are there any special procedures required to prepare the car prior to removing the old battery?

At the risk of offending those with much greater knowledge than I, I was told by another person that to do this, one way is to do it in your garage and to simply hook up a battery charger to the battery clamps before you undo them, making sure not to short out anything. Then just reconnect and remove the battery charger. Also, I was told just to make a little adapter out of a cigarette lighter plug and use a little nine volt battery. I was told this will maintain the voltage enough to retain radio presets, and your coding on the anti theft.

Hope this helps.

If you have a battery charger or other 12 volt DC power supply, you can hook it up while the battery is changed and nothing will be lost. You could also use another 12 volt battery or jump to another 12 volt car.
Make the connections away from the battery ,not on the battery terminals.

P E H

If you do hook up an external power supply of any type, make sure you get the polarity right.
P E H

I have just recently done what Ron Miller suggested with the 9v battery and the cigerette lighter plug. When you really need to disconect the power (removing the airbag in my case), this is the only solution. I was reminded to turn the key to the first (1) position. This worked for me, but I didn't test it or read the wiring diagram to see if this must be done.

Safety Tip
 

Please be careful when doing this procedure. If you use a battery charger, or a spare battery, the potential exists to have a cable shift and short to ground, not a good thing. I have never tried the 9V radio battery, but sounds perfect! I'll try it next time I do a battery removal.

Now for the real safety tip. Always disconnect the negative terminal first. If your wrench grounds while disconnecting, there is no arcing, there is zero potential between ground to ground. If you were working on the positive, it could actually weld to the ground and now you have an electrical fire you can hardly extinguish. When reconnecting, reverse the order and connect the positive first.

Always remove rings, bracelets, and necklaces. My fried almost lost a finger when his wedding band shorted to ground and turned red hot. He still has a circular scar on his ring finger. It's kind of like cutting a section of bark off a tree all the way around!

Good Luck!

Question Update
 

Thanks for the ideas so far. Does anyone know for sure what happens if I don't hook up an additional power source before removing the battery? Will the radio code be the only thing lost when the new battery is installed?

[Edited by Bob I on 11-30-2000 at 08:09 AM]

DEEZEL: Excellent advice!
P E H