It's a much more complicated answer than it seems...
Yes, it has 80A fuses, but fuses are a long way from actual current draw when in use -- besides, fuses take time to heat up and open. That's beside the point.
On the surface -- it can produce 900w rms at min impedance. Digging a little deeper -- being class D assume it's ~80% efficient. So to get 900w out, 1100w+ would have to go in.
Then assume you'll get ~13v from your alternator. Power/Voltage = current -- That's 86A.
Then there's the issue of what signal you're playing. That amp will only approach 86A on a constant basis if you're playing test tones at full volume.
Actual power output of the amp will vary drastically depending on music type and volume. Some music only requires 25-30% test tone power. There's NO music that will get you close to max current draw constantly. However, you will likely see momentary spikes that high at high volume.
With all that in mind -- At low to mid volume, I'd guess ~20-25A. Mid-high volume, 30-50A.
A while back I was having elect probs in my car. The auto elect specialist immediately assumed my system was the cause. They hooked up a professional quality meter on the power lead to my amps (1200w rms). I put in Bass Mekanik and blasted it. It was drawing 50-60A.
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Thanks man 
