[brucepick]

I think the alternator's reduced-charging mode is actually a not-charging mode.

A lead acid battery has a "resting" voltage of 12.5V. It will usually settle there if there's no load, or a very low load, like just the computer + maybe the radio running. With alt not charging, it will then gradually drop over a minute or two. A deep cycle battery drops much more slowly. Once the battery voltage has dropped to whatever the ELD circuit's low voltage limit is, the ELD reactivates the alternator to charge the battery.

So I suspect the ELD circuit cuts the alt's output, and the car "coasts" on the existing charge in the battery. In normal use (not with an alt delete mod done to the car) the ELD only cuts the alt output intermittently, so in between those outages the battery is getting topped up.

Non-charging mode is only available if these conditions are met (I tested and watched carefully):
Speed below 50 mph
Headlights off
Battery topped up
Heavy consumption accessories not running (example, fan on speed one is OK, but not speed 3-4)
Car NOT coasting in gear (ELD is programmed to take advantage of the "free" energy of the coast, and will use it to charge the battery)


So in normal driving, it will cycle in and out of not-charging mode as conditions change. Battery is slightly depleted after startup, and the alt charges normally till it's topped up. The ELD circuit can sense the current "drain" presented to the alt by the slightly depleted battery that powered the computer + clock all night, and then started the car.

When hypermiling, with EOC and DFCO and whatever other methods, not-charging mode will also cycle on and off based on the same requirements.