How do i connect another battery in my truck. Do i just run neg to neg and pos to pos from one bat to the other?
Keep in mind, the battery only supplies the audio when the truck is turned off or for long sustained bass notes - for most usage the alternator will power the audio.
For general usage (or if you wanted to power off-road lights or a winch or similar), yes, you would connect it like you said.
For audio - it is best to run the audio off the second battery alone and use a battery isolator like this so the second battery can't drain the starting battery.
Hope This Helps!!!
2002 Ford Focus Sony CDX-GT410u Sony XT-100HD HD Tuner Stock speakers, no amp, no subs
Yes all you have to do is run positive from one battery to other in trunk and negative of battery in trunk to a good ground. Ive ran my camaro this way for 8years now and it helps the bass emensly. Also when my alternator blew I was able to drive 70 miles on the battery power alone. That is with all sterio or heating off of course but had to run lights because it happend at night.