Freewill

The stock Jeep alternator is supposed to be 140 amps. If the OEM demand is 60 amps then you have 80 amps to play with if you are comfortable loading the alternator to 100%. (I wouldn't on an ongoing basis.)

80 amps is 1120 watts, assuming the loaded alternator puts out 14 volts (reasonable). FYI, 500 watts of light is continously 500 watts, but a 1000 watt stereo does not draw anything close to 1000 watts continuously, even when playing loud.

Battery capacity does not come into play unless you are using more power than the alternator can deliver, or if the engine is off. Anytime you depend on battery capacity you are looking at a very limited time line. That time line is longer when the engine is running, and it is longer with a new top-of-line battery than with a 5 year old stock battery, but it is always limited.

westchester

Whether the alternator can or cannot restore the battery juice as fast as you burn it with multiple lights, adding dual batteries are great insurance to ensure your rig starts and will get you home.

I put in dual yellow-top optimas on Benchmark's dual battery tray, with the 2nd battery hooked to five offroad lights, a 12-volt camping fridge and a winch. The 1st battery is hooked only to the Jeep's stock electrical system, thus always ensuring enough juice to start the engine, power the stock electrics and prevent an unplanned extra night in the boonies.

This way, the stock alternator has sufficient time to slowly charge the batteries back to 100% on the drive home.

MrDillClinton

I'm trying to figure out how you could possibly be lacking in the light dept.

Freewill

X2 on X2 batteries!!

Trappistmonk

Thanks for all the feedback...great info.

C2U5H

This.

I have no idea how much operational amperage the 3.8L JKs draw, but you'd need to add a good bit of lighting to overdraw. As Freewill said, assuming your computers, relays, stock lighting, etc. are drawing 80 A total (which is probably an over-estimate), you have 60 A / 1,120 W left for aftermarket draw (W = A • V, assuming alternator output ≈ 14 Vdc). That's roughly five pairs of 100 W lights.

Adding a dual-battery setup will ensure you'll always start, but if you draw near or over 140 A total you'll always be running a negative charge. Granted, this is only if you ran with all your lights on, or winch plus lights, all the time, which you wouldn't be realistically doing.

SlowJK

If you are going to go dual batteries for the love of baby Jesus don't even consider the yellow tops. If anything go to sears and get the the Die-Hard platuimn group 34. Its a re-badge Odyssey battery which is one of the best companies in the market today other that Deka. Plus they use all the space in the battery and not 6 cylinders (cylinders in a rectangle leaves empty space that could be filled with matts and etc).


Upgrading the ground AND the power output wire from the alternator will make things happier to. If you do use the Dual battery setup make sure to use the battery isolator (The smart one)

hombredelassrtas

Not arguing for or against but why no optima yellow top for dual? I've been running 2 yellow tops for 4 years in a car with massive audio and a tiny alternator.