OBD2 ELM327 scanner

Hi, I've just got one of these fellas working, yay, just wondering about leaving it plugged in all the time. It does have a power on/off switch on it, but still not sure. Any ideas? I suppose I will run a parasitic drain test and see, but what experience do you guys have? Thx.

I have my Scanner plugged in constantly and Its been stood all winter apart from starting up once a month and its no problem, but I have a large battery reserve on my diesel so not sure if this will drain more on a smaller battery unit?:unsure: