I am considering a POC as an alternative to the M6 tanks. My oxygen company has obtained insurance authorization to rent a POC and they told me the units they rent actually weigh about 2 pounds more than the M6 tank. Obviously this is not going to make mobility any easier.  If I purchase something like the Inogen One G3 myself, should I keep the stationary concentrator as back up? I would like to hear how others who have a small POC manage. It seems you should have a backup system, but if you are travelling how do you do that? Any advice or tips from others will be much appreciated. I will feel so much better when I have more confidence to travel other than by car. I have a system for that pretty down pat. My other question is how long can you go out with a POC? I can be away from home for about 6 hours on an M6 tank with conserving device. I think I've read that POC will last about 2 hours without charging. Is this accurate?