Batteries are rated in Ah (eg 110Ah) but will accept only a current draw/load of 20-25A. Thus 2 batteries can only draw up to 40-50A if that current is available so a 150A alternator will barely feel the load.

oh - really tnx for this golden info - I got it now

The L322 Range Rover's alternator controller adjusts the output up to a maximum of 100A PER HOUR.
If the 140AH second battery is (ab)used down to 60% (85AH remaining) the alternator will put back most of the 55AH in about 90 minutes of normal driving. (Assuming DC-DC high current charger to second battery and battery chemistry is modern Cadnium re-inforced lead plates for rapid recharge)

But wait ... shouldn't 100A output put 55AH back in ~35 minutes? Well yes it would if only the second battery was connected, but the max 100A has to recharge the starting battery, run the car and any ancillaries (like a radio, etc) AND the engine revs need to be moderately high for the maximum output and the battery must be able to absorb the high charging rate. So 90 minutes averge driving, or several hours of stop-start city driving.

bye. 2003 TD6, EGR delete, vortex crankcase breather update, performance chip, UHF 2 way, Android head unit, crash camera on dash, always-on rear view camera to mirror screen, LED DRL`s, Electric trailer brake controller. FSR replaced. Pulling 3T caravan all about Australia