The reason I personally recommend the HO over bigger or dual batterys "IF" you can afford it. When I installed my D3400 and D1200 in my car with the factory alternator I though it should cure most of the headlight dimming and voltage drop, Well it didn't. After a minute or two of hard playing and the voltage on the dual batterys dropped and could NOT recover until I turned the volumer down and let the factory alt catch up and recharge the batterys. With that being said, the XS Power batterys are VERY FAST at recovering, which is their claim to fame, So they did do that VERY WELL. Now the reason a HO is better is, the batterys can only maintain high voltage for a short time before needing recarged, BUT the HO can maintain high voltage continuosly by its self. Which do you think is better? Now for the math part, If your amplifiers are demanding 2700 watts or 270 amps (amps x 10 = watts) If you have a 270 amp HO alt you in theory don't even need the battery except to start the car. In real time the battery banks are re-inforcement for dymanic peaks. With all that being said, your amps aren't demanding 2700 watts except at full volume, So realisticly at normal listening levels they are drawing alot less So this is why a stock 130 amp alternator is good enough for most ppl. IS because between the 1300 watts the alt is making, the amplifiers are only using what they need from the battery(s) to fill the void. A good battery is always important also, and if your factory atlernator is keeping up except for the very occassional peak the your probably are good investing in a few better batterys first. I think the reason "most" ppl buy batterys is that its usaully cheaper and they can be added as the budget allows, as with the HO alt, its one BIG LUMP all at once. So my personal advice to you, Jaycee is the same you give every body else, watch your voltage after each upgrade and see what really works. If you can only afford the battery right now, then thats better than nothing and you will want to upgrade the batterys sooner or later anyways even if you did get the HO first. If I could go back I would of did the HO first and I bet I would of only needed one good battery under the hood. BTW I have another vehicle with a Powermaster 200 amp alternator and Warn winch, let me tell you Jaycee, When I installed the HO I experimented with NO batterys and used the winch with the headlights on and they never even change brightness just stayed even kill even with no batterys and turning the winch motor on and off, over and over, VERY IMPRESSIVE. You must have POWER to make POWER.