I don't understand why you would want to keep the battery from being recharged while accelerating if the SOC is low? That is when I try to accelerate slower if I can so I can charge and get up to speed at the same time.
Because you don't necessarily want the battery charged. Remember that charging the battery is using extra gasoline. The idea behind a hybrid is to recapture lost energy (regenerative braking) and, to a lesser degree, to run the ICE as efficiently as possible. So, for example, when running at a steady rate of speed on the highway, Ford knows what RPMs the engine runs most efficiently -- for example, bumping the engine speed from 2000 to 2200 RPMs might use little, to no, additional gas (this is merely a demonstration, I don't know the efficient points of the engine); so it it is more efficient to run the engine at 2200 RPM and use that slight increase in power to charge the battery.
By contrast, when you are accelerating, you are above the RPMs where the engine is its most efficient. Slowing down, so you can charge the battery, tends to make your acceleration even more inefficient; any charge you are adding to your battery is costing you MPG because of how hard the engine is working. Instead, the idea is that accelerating faster, so the battery does not charge, runs the engine harder for a shorter length of time and, while you are using more energy, short term, to get to speed, you are saving energy because the engine runs efficiently for longer.
At least one argument made by hypermilers is: since all battery charge is created by use of gasoline, and you are losing some energy by converting the power to electricity and then charging your battery, you want to charge the battery as little as possible. It can be debated how true that is, but it is worth remembering that you want the best fuel efficiency, which isn't always the same as running in EV mode as much as possible.
Edited by raadsel, 28 April 2015 - 08:57 AM.