71 MPG US = 3.3 L/100 km
New this tank: about 90% was with the alternator disconnected, which in this car is MUCH easier to do than in a Metro/Firefly. Simply disconnect the field control/charging light wire connector from the body of the alt.
Tank MPG was 9% higher than the previous tank, with many of the same trips. That said, it was in fairly warmer weather. So I figure the alternator delete is about a 6-7% gain, conservative estimate.
The big [used] deep cycle batt I'm running seems to be good for around an hour of driving [with about 10 minutes of lights on for safety in that hour] before voltage under load drops to ~11.8. Below that level, the engine seems to run a little rougher. [Ha, how can you tell...]
Daox has experimented with this on his Mirage as well:
alternator delete on my Mitsubishi Mirage.