Do not disconnect your alternator to reduce electrical load like this guy:
he charges his battery separately before driving. That's one
inconvenience, there is one big problem, in 1-2 hours your car will stop
running. Your battery power has to be strong if you want higher fuel
efficiency because it needs at least 55 amps to supply for your vehicle
ignition system (fuel pump power consumption included). Remember Weaker
power = Weaker combustion.
For only 4% of a hybrid cost, OFS can turn any vehicle into a hybrid-like
vehicle. If you haven't tried it, do not discount it.