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2nd battery to add to my system not sure what to do I’ve been told 2 different things and don’t know what’s true

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Hey I’m currently doing a car audio install in a 2018 Kia cerato YD /forte 3 and I need some recommendations on that to do I’ve done some installations before but none with a dual battery set up I’m planning on using a 200-250a alternator and a slimline 170AH AGM in the back I’ve heard some people say just use a isolator whilst someone from a car audio shop says to use a regulator or Dc-dc charger I’ve looked everywhere for a reg or dc-dc that is 200-250a to keep up with the power draw from the 2-3kw monoblock I’m planning on getting i already own the battery and the sub but no idea what to do after the advice that if I don’t use a dc-dc or reg my battery might get too much charge and go short circuit and act like a welder so no idea now what to do 


idk if I’m allowed to post links 

link to the alternator: 



theres also a stinger alternator that’s a 220a but I don’t have a link it would be custom made 

ive asked mechman they don’t sell a alternator for my vehicle and as soon as they knew they don’t have one they wouldn’t reply to any questions about battery systems 


Cheers Rick 

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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.

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Sounds like theyre trying to upsell you on equipment thats not needed. 

An isolator is typically used to prevent parasitic draw or for running your system with the car turned off so it keeps your main battery charged. If youre using two batteries with similar resting voltage, which they should be since they are both lead batteries, an isolator is not necessary. Ive never heard of someone needing a regulator or charger for a second battery. Just wire the two batteries in parallel and send it. Like chevyboy said it would be best if they were both AGM but having one AGM and one flooded cell shouldnt cause any problems. Overcharging would only be a concern if your charge voltage is too high, the current draw will drop to near zero when the battery reaches a full charge. 

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