be someone who has blow a ECU when changing the battery on a friends p38 .

I need to do a full service of my wife's P38 but is there anything I need to know beyond a stock oil change.

Reading fault codes could be good, but unless there are fault messages it is unlikely.
I have my own BlackBox kit. Other than that, if you disconnect the battery from both
+ and -, when you reconnect have the key in your pocket and the drivers door open.
Otherwise the locks will automatically go into Fort Knox mode, as soon as the + is reconnected.

Everything else would be like servicing on your LSE.

Cool thanks

All I need now is a service kit

@Jules. A trick I have used when changing batteries on 'sensitive' cars is to use a fully charged 'jump pack' as a temporary supply for the ECU etc.

Connect the earth lead of the jump pack to a good earth on car and the positive of the jump pack to the positive battery clamp/lead. You can just about undo the battery lead with the jump pack connected.....you need to make sure it stays connected. This will act as a 'keep alive' for the ECU and alarm and it will be non the wiser

Take your time cos it's not easy to juggle everything, but if you work on different cars and are not sure what to expect then it is a good 'better safe than sorry' option

I have changed batteries on both my 4.6SE and my girlfriends 2.5DT without any special precautions and didn't experience problems afterwards. It is a bad idea to leave the ECU's without power for a porlonged time (I kept a power feed to it during the engine rebuild for example), but for short work (welding, battery/alternator replacement...) you should be fine.