Article: If you have a 3000w amp playing three 1000w subs, but they really sound weak, then it's time to get more power. Alternatively, play the bass as loud as you can and see if your dome lights dim or not. If they barely flicker, then your power is manageable, but if they almost go dark with each bass note, then it's time for more power. Although wet cells can be used, they could spill battery acid in your car if they leak. Dry cell batteries are a better choice if you can afford them. Dry cells have no battery acid and are extremely safe in a vehicle.   Connect the batteries in the car with a large ground wire and ground it in metal. You don’t have to run it into the engine bay; any good metal ground will do. Be sure to put them in a sequence: first battery connected to the main in engine bay and last battery connected to the amp(s). By getting a larger alternator that puts of more amperage, your battery will be continuously and quickly charged. Whenever massive amounts of power is needed, it's directed from the alternator much more than the battery, giving you more power. A good 220-amp alternator can really make a difference in sound quality and bass. You just have to find it for a good price and have it installed.

What is a summary?
Determine whether you need multiple batteries and capacitors. The cheapest way to fix a major power problem is with more batteries. To install multiple batteries (or capacitors), connect the main battery in the engine bay with the another one elsewhere in the car that has a large, low gauge wire (like a 4 or 2). Systematically connect the next battery by running a wire from the first battery power, to the second battery power, and so on until you reach the last battery. Connect the last battery to the amp(s) with a separate wire. You can upgrade your alternator, if you don’t want numerous batteries or capacitors to take up space in your car.