The point of the mosfets is that they can be electronically controlled to regulate voltage. The circuitry in the regulator fires the mosfets at different phase angles depending on the voltage output from the stator in order to convert the three phase AC output from the stator into a regulated DC voltage.The point of the mosfets is to handle excess current for much larger bikes without wearing out.
These regulators are meant for bikes with permanent magnet alternators where control of the field coil is impossible so voltage regulation must happen electronically.
The Turnigy batteries look to be pretty robust little guys. Looks like hobby king has 4 cell versions all the way up to 10Ah.The lithium graphene battery can handle more volts than a functional regulator will put out.
Once it's charged to the charging voltage the current should just pass through the battery and since the graphene batteries have nearly zero internal resistance this shouldn't produce any heat.
Could be a good alternative to AntiGravity batteries.
The problem below 5000rpms isn't that the voltage regulator isn't trying to charge the battery, the problem is that the entire alternator physically does not produce voltages high enough below that speed.I suppose my main concern would be the feild coil and stator. I'm worried since the stock regulator rectifier isn't charging at rpms less than five thousand that keeping the stock regulator will continue the same problem.
Below 5000 rpm, with the battery presumably discharging, the stock voltage regulator would be outputting its maximum rate but the rotor just isn't spinning fast enough. It's only when the rotating field cuts the stator windings above 5000 rpm that the generated voltage exceeds the voltage required to charge the battery.
Changing to a modern voltage regulator or removing the stock one will have NO effect on the voltage output below 5000rpm other than possibly being more efficient by virtue of being newer and made to modern standards. Might mean that you'll see the required voltage generated at a slightly lower rpm. Maybe 4800 instead of 5000.
The 50W is a rough approximation based on (14.5^2)/4.04 (stock field coil is 4.04ohms) and is almost all heat. There's no simple formula that could accurately calculate the power consumed to generate the magnetic field, especially in our type of alternator with its mutual-mutual-induction design, but I'm sure it could be deduced by observation with the right equipment.50 watts of power in the feild coil doesn't mean 50 watts of heat. I'm assuming most of that is turned into a magnetic field and only the current lost in resistance turns into heat. A fraction of 50 watts isn't much heat.
In any case though, it's heat in the field coil which is dissipated pretty well into the engine casing. It's no more heat than it sees when the bike is running and charging a depleted battery, but it's not meant to be doing that all the time. Especially with our aging components I'd want to reduce any stress on them, not increase it.