I am a working professional and also own the SB-600/SB-800. Recently I bought a new SB-900 and use it with my Quantum Battery 1+ packs - I have not loaded any batteries in it yet. When I went to use it like I did with my SB-800 the thing shut off (thermal warning) after 15-20 mins of what I consider 'light use' as a fill. It was during a wedding so I was a bit concerned that Nikon's flagship speedlight became so useless so fast. I grabbed my SB-800 and finished the job. After a bit of online research I find that this is a common thing and is due to "user error" not a design flaw. (HA!) I love the 900 due to the flexibility with the button placement..etc. I do not use on camera flash much at all and if I need any external lighting I use my Lumedyne system and Pocketwizards. Out of 1000 shots I might use the on camera flash for 100 or less of them - and it is for fill only. When I need it, I NEED IT and will not accept waiting around for it to cool off. I am a bit concerned about if I should keep this or not and return it. I just thought that Nikon's top of the line flash would function a bit better than this. For now I have the thermal warning turned off and hoping that I do not melt the thing but my SB-800 has been a workhorse for years and I have abused that flash without one problem. Is it worth keeping the 900? I need all the space I have in my gear bag and do not need a sketchy item getting in the way. Should I trust that it will function properly with the thermal sensor turned off? It seems like maybe Nikon is only trying to implement a warning system to keep from making a lot of service repairs but honestly with the thermal warning on it is far from a professional item. Maybe the SB-700 is a better unit for me? Is it prone to this as well? Maybe a different battery system would be better? Oh, and BTW - Nikon support S-T-I-N-K-S. I knew more about the flash than they did.