Haha it takes a little time to get the hang of it. Also if you google something, add "car audio forum" to the end and it will search this forum as well as other car audio related forums //content.invisioncic.com/y282845/emoticons/biggrin.gif.d71a5d36fcbab170f2364c9f2e3946cb.gif
If you don't have a budget, get XS Power or NorthStar. Those seem to be 2 of the best brands from all the battery comparison videos I've seen. However they are usually the most expensive.
Can you fit a XS Power D3100 under your hood? Or what's the biggest size you can fit?
The D3100s are about $370 and can power around 4-5k watts (4K watts if it is your primary battery or 5k watts if it is your secondary)
Take a look at this chart
Wattage Chart - XS Power