When the ECU is disconnected all the parameters are reset to default.
The Ecu can relearn over a very short time and the only odd things that you will experience should be:
The A/C defaults to ON at 25degrees.
The idle will be a little on the high side as the info from the stepper motor IAC is established.
You may experience the idle speed of 850rpm to stabilise more slowly for the first couple of runs
The engine will run fine and you should not experience any problems whatsoever.
I find reseting the ECU very handy when I switch from SUL to SUL|PLS|octane booster, as the car 'unlearns' the low-octane petrol and gets stuck in with (almost) 100octane good stuff.
Works a treat http://www.ltregister.f9.co.uk/graphics/Happy.gif border|EQU| 0 align|EQU| middle >
Idle is a bit bizare for a couple of stops but nothing else.
I had to do this a couple of times when the AAA ever-ready that passes for my car battery went flat after I left the car for 10 days or so without driving. As far as I can tell there have been no adverse effects. The CD player rest itself and lost the presets after doing this but this may be a separate problem.
Presumably the battery has to be disconnected for certain types of maintenance/repair work and I can't see that they would design it so you could not do this. I wait to be proved wrong...
I had the battery disconnected when I had the AYC fuse-link removed. There was no other way to remove the fuse-link without having to disconnect the battery first. After it was removed and the battery reconnected, the only thing I needed to do was to preset all my radio frequencies again. Immediately after this was done and when I drove the car I did hear some funny noises coming from the passenger side footwell or there about. The sound was like buzzing and short-circuiting only for a moment. Apart from that, it did not have any adverse effect on the car and infact I took it up to about 145mph @ about 6,500rpm with the AYC fuse-link removed. Mind you the car was still going hard!!!