Use the search tool for big 3. You will find a ton of information and it will help you learn what to do.
You can make sure your amp gets 14.4v by upgrading your alternator.
Batteries store a power, your alternator makes power.
Your batteries store power up to around 12.8v
Your alternator makes power in the range of 13.8-14.8v depending on your vehicle.
You can get aftermarket alternators that make more current then your stock alternator does.
An example would be keep your stock alternator which is probably around 80 amps, you could use an amp that will push 800watts.
if you upgrade to a 220A alternator you could run 2200watts.
This is just an example to give you an idea of how large your alternator needs to be to stay at 14.4v
How many watts are you looking for?