The re-learning process is definitely NOT a myth. If your engine is in a "new" condition, then the ecu wont have to adjust to anything, but with the modifications ive done in the past, you can actually feel and see the ecu learning. To get the most out of the injectors, i had to turn the fuel pressure up to around 3.5 bar. That obviusly shortens the injector timing, but when you reset the ecu, it geos back to the 2.7bar settings, so runs really rich, and you can see it on the air/fuel ratio gauge. Once the ECU has adjusterd, it starts & drives like that until the battery is disconnected and it has to learn again!
With regards to the battery ampage, a larger amp battery lasts a lot longer without charging, or inbetween charges. The clue is in the name, ah stands for amp hours! So in theory, a 25ah battery should go for 1.67 times longer then a 15ah battery, providing they were both drawing the same power. But the puma, with all its electrics, lights, fans, alarm ect, is reccomended to have a 54ah battery, and that only lasts about a week and a half without charge, and i dont want to have to take the battery out to keep trickle charging before i use it, so i think steve is right, im not going to be driving this car every day, is will just be a weekend car, so its probably not a good idea to fit one without an isolator switch unless you are prapared to keep charging it when you dont drive it for more then a few days.
The less mods you have, the less problems you would have with the ecu resetting itself, but you would still have to re set the clock every time you wanted it right, and you'd still have to re set radio presets and settings every time you wanted to use them. Its only small things, but i had a stereo wired into my car with no perm live, and had to do this every time i got in the car, and it gets really annoying having to keep doing it, rather then it just coming on as you like, with your favourite station playing.
So even a 25ah battery wont suffice, i dont think ill settle for anything less then 45ah.
Cheers for the imput though guys, nice to get other peoples experience/advice on things!