I would say from popular vote, its a personal vote between option 1 and 2Well that money saved will either be spent on the alt upgrade or another G31, more than likely.
DC Power 270XP
Diehard Platinum G34
Diehard Platinum G31 x2
Advantage: Cost savings
or
DC Power 270XP
Diehard Platinum G34
Diehard Platinum G31 x3
Advantage: Extra G31
or
DC Power 370XP
Diehard Platinum G34
Diehard Platinum G31 x2
Advantage: 100A bigger alternator