lights dimming and not the alternator?

my trucks lights dim from the beat of my mid amp, gotta love a inefficient class a/b, but i have 14-15 volts when driving and the lowest it will get is 13 when i have been parked for a while. my question is, how big of a difference will a deep cycle batt make? i have been using regular batts because i get them for almost nothing but have been having to replace them because they wont keep their charge. im cheap so i wait until i have to turn my stereo off when i start slowing down before pulling into the driveway/parking lot and rev the engine for a bit so the truck will start in the morning. i also live in vermont so the cold makes it hard anyways

Get the battery and alt load tested.   The alt can put out 14 volts, ,but not the amperage it should, , thats how my past alts have died, the voltage stayed up, but the amperage output declined.2003 Chevy Avalanche,Eclipse CD7000,Morel Elate 5,Adire Extremis,Alpine PDX-4.150, 15" TC-3000, 2 Alpine PDX-1.1000, 470Amp HO Alt.

get a capacitor buddy

Sounds like you do have either a battery or alternator problem. As far as adding a cap, I wouldn't. They don't help with the problem you are having. They are a waste of money in my opinion.'85 Toy

If you need a new battery I would go with a deep cycle battery, (yellow top). much better and will handle the deep discharges, you could also consider the big 3. and ensure all connections are clean and tight

No, a capacitor will NOT help.  If you have measured your voltage and it is not dipping but the lights dim, then where are you measuring the voltage?  Are you reading the voltmeter in the vehicle?  That won't tell you the whole story.  Use a DMM and test the voltage at the battery, at the amplifier, at the headlights, etc. and let me know how it changes.  If the lights dim, the voltage must be dropping.....Support the12volt.com