Nige and I were discussing giving CA3 its own power supply to speed up reconnection with an ECM. Here's some answers: How much power does the CA3 draw? It draws between about 140 - 170 mA at 14v whether connected to an ECM or not. Does the CA3 reconnect any quicker if it retains its power? It depends. If the ECM is disconnected from the CA3 by cycling power, it reconnects quicker. If the ECM is disconnected by the software switch in ET, it still takes a while to reconnect. A standard 9v battery is about 500mAh, two in series 1000mAh so we should expect two or three hours run time, bearing in mind the CA3 needs 12v to work. This assumes the batteries can handle the inrush current which I don't have the wherewithal to measure ATM. To make a semi usefull battery pack will take a couple of 15 pin D sub connectors and a bit of soldering and I may give it a try if I get some spare time. It could potentially be useful in some situations.
That pretty much equals my experience. If the CA remains powered throughout and the ECM is simply powered down from the keyswitch without disconnecting ET software via the connect/disconnect button then the reconnection is quite quick, far quicker than what it would be if the ET connection had to be re-established again from the laptop screen.
My next step is to check whether or not the DEF ECM that is under discussion will re-read the active codes with a quick power cycle, or just reconnect and retain all the "old" data. In my mind I can't now leave this question unanswered so I'll fabricobble something together and go and find a faulting DEF system to try it on. This may take a little time.