Leaderboard

You can wire the second battery in parallel to the existing battery. The main concern typically is the difference in battery technology (lead acid as OEM and AGM for aftermarket). In reality, there isnt anything special you need in between the stock battery and the new AGM. The only suggestion I would make is in a few years when the stock fails (due to age and use), to replace it with a like in kind battery to the AGM. Your battery wont get "too much charge". Alternators only output to what they are asked. If you arent blasting music, they will have a low output to supply the bare minimum the car is asking for (A/C, lights, radio, etc.) and when you crank the volume it will output more as it sees a larger "load" and output as much as it can up to 220a to do whatever it can to try to maintain good voltage.