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I have heard that I can replace my 2006 3.0 Z-4 battery without loss of programming by installing a trickle charger prior to changing the battery. I have a Schumacher battery charger that has a 3 Amp maintain setting. Could I hook this up under the hood and change the battery safely?
 

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It depends on the charger. Some chargers rely on a battery being in the circuit to maintain the voltage. If you connect a trickle charger that isn't voltage regulated, you may get an over voltage condition when you disconnect the battery.
The only thing you should lose is the window position settings when you disconnect the battery, and they're easy to reset. Put the window all the way up and continue to hold the button for at least 10 seconds. Put the window all the way down and continue to hold the button for at least 10 seconds.
 

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I replaced the battery in my '03 and it had no power for approx. 10 minutes and did not lose any presets other than time.
 

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If you have a digital multi meter or volt meter measure what the output voltage of your trickle charger is without the leads connected to anything. If it's in the 11-14 volt range you should be OK to use it as back up power.

If you do use this method, remember that the positive battery cable is HOT because you have your alternate power source connected, so don't let it touch the car body or anything else that's a ground.
 

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It depends on the charger. Some chargers rely on a battery being in the circuit to maintain the voltage...
I tried connecting my Deltran Battery Tender (also sold with BMW labels) when I replaced my battery on my Z4. After I disconnected the battery, the charger shut down.

As others have pointed out, it is no great whoop to disconnect the battery. The radio does not lose its presets. You have to set the clock and initialize the power windows. Bonus: Disconnecting also resets the ECU so the car runs a bit faster until it re-learns your driving style.:drive:
 
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