A good way to determine if the battery is ok for you to turn off main line voltage is to open up the car station and use a meter to check the battery voltage. set on VDC, and place one lead on the ground connection of the CLC board, then look for the Diode a little above and to the left of the battery, it is D4 I believe, put your other meter lead on the anode of this diode, it should read 3 volts which is the voltage of a new battery. I usually see this around 2.7 volts and can turn off the power without reprogramming the CLC. I am not sure how low this can be before you lose the program, but i think above 2.5 should be fine. Just one last note, we obtained a dover contract a few years back with 8 dmc units, we lost the program on the first 2 cars we shut off for service, after investigating further I found that the D4 diode had been cut out from all the CLC boards on the job. sabotage