[GriffinRU]

Originally Posted by lutach

I would try one of the following:

IRF2804 (Just seems to be a monster of a FET and it has lower resistance and 40 volts to be on the safe side)
IRF2903Z (Same voltage as the stock unit, but lower resistance and 20A less than the above mentioned)

I will agree with Lutach, IRF2804 is a good choice. (IRF1404 not bad also)
IRL3803 is not a stella performer, but cheap.
The only place I would worry is boost-charge capacitor, replacement FET's have higher gate capacitance by 10-15% and require more charge.
But in general with T0-220 package you cannot draw more than 75A from FET, so the lower Rdon in this case better.
Just do not short FET's mounting/heatsinking tabs!