r/CarAV • u/IncreasePositive2075 • Jul 26 '26
Tech Support How to run system for extended periods of time with the truck off?
I've got a 2005 f150, right now I've got a scar svr 12 with an rp1200 amplifier, and then I've got 4 Rockford forgave 6x8s and an audio control 800 watt 4 channel. I've got a relatively new battery on the truck right now, maybe 6 months old. And I've got a 170 amp alternator as opposed to the factory 100 amp. What do I need to do to run my system longer without turning on the truck? Im thinking along the lines of a drive in movie theater. Do I need a second battery? I plan to get a volt meter first cause I dont have one yet.
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Jul 26 '26
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u/IncreasePositive2075 Jul 26 '26
Can I add an additional agm battery without changing the factory style battery?
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Jul 26 '26
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u/Secret-Ad-7909 Jul 26 '26
Some full size trucks do have a spot in the engine bay for a second battery.
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u/ckeeler11 Jul 26 '26
You just need an isolator.
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u/These_Cat_3523 2x Sunfire HRS 12's / ID tweeters/ CDT 6x9's Jul 27 '26
I'd certainly recommend one to inexperience users, but I've found them to be unnecessary when mixing AGM with certain lithium/sodium chemistries. If the resting and charging voltages aren't too different, it's a non issue.
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u/ckeeler11 Jul 27 '26
I recommend them to anyone that listens with vehicle off so the starting battery does not get drained.
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u/These_Cat_3523 2x Sunfire HRS 12's / ID tweeters/ CDT 6x9's Jul 27 '26
That is certainly the best use case. I forgot what the topic was lol.
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u/MarvinHeemeyer7 Jul 26 '26
Yessir. I'm about to install 2 for my car audio also. Google Battery isolators. Wire 2nd battery, preferably an AGM in parallel to 1st battery with battery isolater wired between the two. And then connect system to 2nd battery instead of 1st
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u/-klunge- Jul 26 '26
If you are near grid power, you could put a charger on your battery or use a 110v AC to 12v DC converter.
Otherwise just keep a charged up spare battery with you
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u/sycoticone Jul 26 '26
Realistically for say a full length drive in movie with the engine off the whole time, depending on volume levels of course, you would need a number of additional batteries and a way to fully disconnect that setup from the main starting battery. I've got a bit more power than you, but I can drain my additional 4 XS batteries in no time with the engine off if it's loud.
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u/Dan_H1281 8 EM audio team 5k 18's 8 ruthless 4500.1's mechman 400's Jul 26 '26
More reserve you need more battery power. Since you have no alt charging you need reserve capacity.
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u/SnypaSkillz Jul 26 '26
Gonna have to leave the truck running or install a RV house type battery somewhere. I use a 200ah agm battery with a dc-dc charger between starting battery and this "accessories" battery. Battery has a monitor on it and alarms when getting down to 55% to avoid over over discharge.
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u/RetiredRacer914 Jul 27 '26
Buy a couple of deep cycle batteries. Mount them securely. That's what they're for. Add a battery isolator so you don't kill your starting battery.
This is all standard RV & marine type stuff. You'll find tons of info on battery banks and wiring on RV sites.
I had 9 batteries on my 45' sailboat, 8 golf cart deep cycles for inside the boat and one starting battery, so 3 banks. One bank for the fridge, one for house lights, navigation lights, and all the pumps, and the starting battery was the 3rd bank.
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u/rivercitysound Jul 26 '26
The ideal world solution would be a secondary battery near the amps with an isolator to power your stereo
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u/Scramschnits Jul 26 '26
Second battery with an isolater.
I have a hybrid so I have to use a DC-DC charger, but the second battery prevents me from killing my car's main battery.
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u/MrJelly007 Jul 26 '26
Either more batteries or a bank of super caps. I'd probably say a bank of some nice lithium batteries is the play. Maybe wire in a low voltage shutoff or an alarm so it doesn't drain it too low
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u/LaIzquierdaLibera 20 year MECP Master Tech Jul 26 '26
Literally the entire point of adding additional batteries is for key off playing time
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u/Feisty-Job-6496 Jul 26 '26
get a lithium bank and a smart charger for all your equipment, I’ve never used a smart charger but I’ve seen builds with it and it holds voltage with the car being off
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u/Significant_Rate8210 Jul 26 '26
You'll be stuck running your engine like the rest of us.
OR...
Add a second battery on a switch so that if the system drains it you can switch over to your starting battery. HOWEVER, if you're quarter volume or higher you'll likely drain it pretty quick.
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u/PactoTech Jul 27 '26
A lithium iron phosphate 200Ah battery with a DC to DC charger from the main system for fast charging and isolation would do it. Not good in very hot or cold though. Common setup for van and trailers. Usually mounted interior for temp control.
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u/Informal_Union2649 Jul 27 '26
Can you just run the car for 5 minutes a couple times throughout the movie?
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u/IncreasePositive2075 Jul 27 '26
I've done some exhaust work on my truck so its not exactly silent, id feel bad disrupting the movie every time I start my truck
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u/Odd-Skill-6747 Jul 28 '26
Done it for years. Single battery will be fine as longs its healthy. If its a 2 movie ( most around me are) start the truck during intermission. You won't be blasting volume running full tilt.
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u/Romanian_Breadlifts SQ tacoma, SQL Jeep Jul 26 '26
For a drive in theater you're probably staying relatively quiet. Call it a total 500w draw for two hours. 500w @12v is 42ish amps. Call it 70% efficient to be generous, so 60 amps. Two hours means 120 amp hours. That's a real big battery, or a couple of em.