My PluginPrius can offer up about 1000 watts out of the smallish 12 volt accessory battery. That seems to be the limit of the converter, that works off the big traction battery. I have not bothered to investigate accessing the big battery directly, don't need to and besides you can do a lot with 1000 watts. When I plug my 12 inverter (Harbor Freight 400 watt continuous/800 surge, mod sine wave piece of crap, but it works perfect, pure sine wave not required for my Luna chargers) into the beefed up 12 vdc outlet (most car "cigarette lighter" sockets are 15 amp, I draw a bit over 17 amps when charging my 52 volt battery at 3 amps) as long as the car is "on", not running the ICE engine but just turned on, the big battery keeps the small one topped off. Eventually the ICE engine auto starts, runs at a most efficient RPM for a few minutes while it recharges the big battery, and then shuts down again. Prius geeks have reported that this process and the fuel it requires, shows that is MORE efficient then any other small gas generator, Honda etc. It's also the quietest and least amount of hassle.
I only use this capability when on the way to a ride, with ebike along, and when camped out. Once we had a scheduled power outage by my local utility and I needed to use my home computer (my grid tie system is battery less by design, so my power goes out when the grid is down, after being off grid for 28 years I like not having them and the outages are so rare it's not an issue) so I backed the PIP near the house and ran an extension cord into my office. The car never started in 2 or 3 hours, so yeah it works great and is a widely unknown advantage of driving a hybrid. That and being able to camp in them while having heat or AC all night while using very little fuel.
BTW: I just bought another HB inverter, same as my first one, for my work truck, and they are on sale right now, less then $20.00!