First thing that was taught to me when we did electrical at trade school, (well they did not mention ecu's as it was a little while ago), voltage spikes or surges can do damage to various electrical items.

I highly recomment the CTEK units to anyone.

Rattter is right, if you are using a crap charger there is every chance that it may ruin your ECU from a spike. But if you get a good charger/maintainer then leaving the terminals connected is not an issue. Only issue I have with my maintain is I cant connect throught the power source socket as without the key on you dont get a connection.

If its factory ford alarm just turn the ignition on then disconnect the battery.... Wont hurt anything

So what does disconnecting the battery (for any reason) do? Doesn't it reset all sorts of computer stuff in the car? I've got a good quality charger and have never boothered disconnecting a terminal. What changes when you remove a terminal?

Edited 27/04/12 02:22 AM27/04/12 02:22 AM by Pete A

ive got one of the projecta units mentioned above, I might go months without driving my rx7 (mostly track use) so it was a PITA having the battery die. Got a charger that is designed to be left on, has a float mode to keep the battery close enough to full charge without doing any damage. Cost me approx $70, well worth it.

So what does disconnecting the battery (for any reason) do? Doesn't it reset all sorts of computer stuff in the car? I've got a good quality charger and have never boothered disconnecting a terminal. What changes when you remove a terminal?

Yes it clears keep alive memory which holds adaptive idle strategies etc, it learns itself again with a short drive, good quality chargers are safER to use with the terminals connected but any surge through an electrical module risks damage to fragile circuits, capacitors etc , same reason you disconnect the battery when your welding on a car etc

most welders simply put a surge protector on instead of disconnecting.