Re: Details, details
I didn't see a manual on Tesla's web site, but the Powerwall packs might only be usable in a grid-tied system from how there marketing fluff reads. The tiny amount of information available isn't enough to make an informed buying decision. I read another article that stated the Powerwall didn't come with an inverter. At this point, they are vaporware.
The best backup battery is likely to come as a kit for a used car pack that doesn't provide enough range anymore, but is perfectly serviceable for a home application. DIYr's are snapping up the used Prius NiMh packs since they are easy to refurbish and not as fussy as Li chemistry batteries.
Somehow I think that P.T. Musk is trying to forestall competition before the Gigglefactory is producing.