batterry+chip

["R. Wiratorn" <withu@loxinfo.co.th>]

        Hi all

                I would like to know if the battery must be disconnected before
        doing a service ?
                 And if the battery has been disconnect, what will happen to
the car's         computer after reconnect the batterry ? Any memory loss ?
Do I have to
        re-enter the instruction codes to the chip ?
                My S4 loss much power after returned from 60,000 Km service,
the dealer
        said they didn't do anything to make it loss of power. I told them
to check for
        any leaks, but they found nothing. by the way, I hear the noise of
the air
        blown off 3-4 times every time when I back off the throttle. I
didn't hear this
        before. Do you thing this noise is relate to the power loss ?
                someone told me that BMW car will loss the instruction codes
if the batterry
        is disconnected and need to be re-enter the codes after reconnect
the batterry.
        I'm not sure about Audi's.

                                                                Thanks 
                                                                K.Ben