I have a 90 amp factory alt and I'm wondering if I need a new one due to what I'm installing?

I have a kicker ZX1500 and I'm going to buy a RE audo 15'' SX

Dominick Iraggi quoted me on a new one made by him at $419 for 220.

I'm thinking maybe I could just add another battery. I just bought a Stinger SPV44 battery. Maybe this battey with the stock battery and a bat isolator by stinger?