If the current flowing from one battery to the other was 150 amps, that would be 150 amps per hour, which would work out to 150 / 60 = 2.5 amp*hours per minute. 2.5 / 6 = .41 amp*hours in 10 seconds.
Even if the current was 600 amps, then it would be 1.64 amp*hours in 10 seconds.
Like I said...not much.
But yea, the Powerstream or other such setup would be a step up over a plain old relay. Not really needed, but nice to have if you've got it. The other view would be that's an additional potential point of failure.
Current: 76 E-250, bubble-top, self-contained|couple of old Yamaha enduros
Previous wheelers: 41 Willys|78 FJ40|78 Bronco|84 Bronco|74 Ramcharger|78 Ramcharger|79 D150 PowerWagon|77 D100|79 D400 dually, converted to 4WD, utility bed, 10' Lance|75 Westy|69 Scout, RHD|bunch of others|bunch of bikes|couple of boats|couple of motorhomes|blah blah|so what|not my idea|just doin' what I'm told|wank wank|this space for rent|candy is dandy|but liquor is quicker