Need advice on dual battery setup with stock alternator - 4th gen 4Runner

[RkyMtnHgh]

Hi all,

I'm new to the board and relatively new to overlanding, but I'm so glad I found this forum. What a great resource!

To the point, I'm looking to add a National Luna dual battery system to my '03 V6 4Runner but I'm not sure what to make of the voltage readings after testing my alternator. Per the National Luna installation manual, "A regulated voltage above 14.0 volts under load is preferable for optimal battery charging." It also says, "when measuring voltage across main battery terminals, voltage should be above 13.5 volts" and "if voltage drops below 13.5 under load, alternator may have to be upgraded".

Using my handheld Radio Shack multimeter, I measured the voltage at the battery terminals as 13.42 volts with the engine running and all accessories off. Under load (A/C, aux lights, stereo, etc., running), the reading was 13.21 volts.

It's my understanding that the stock alternator in 4th gen 4Runners is rated around 130 amps which should be more than enough to handle a dual battery system and some accessories, yet my vehicle's normal voltage and voltage under load are below (albeit slightly) the output recommended by National Luna. What are your thoughts and/or recommendations? Many thanks.


'03 SR5 4WD V6 l OME 884/895 Nitro Sport l LR UCAs l DuraTrac 265/70/17 l Shrockworks Rock Sliders l HIR Lamps l Defiant Light Bar w/ IPF 968 l Yakima MegaWarrior

 

[Mr. Leary]

The alternator does not fully kick in when the engine is idling. Rev it up and you will see the voltage jump to around 14V. If you can, check this with a scan guage. The voltage should rise without "bouncing." If it does, then you shouldn't have anything to worry about.

 

[eli]

You not only need to measure the out put with the proper engine speed (as mentioned above) but take into consideration the age of your battery. 5 years is about max. for a conventional lead acid battery. I'm actually planning my system as well . . .

Good Luck

 

[RkyMtnHgh]

I appreciate the reply guys--that makes a lot of sense. Right now I've got a 6 month old DieHard Platinum P-5 (Odyssey) as my main, but I plan to make that the auxiliary and re-install the 2 year old Toyota True Start 27F it replaced as the starting battery for now. I'll post a build thread after I'm done with the install. Thanks again.

 

[Utah KJ]

Keep in mind also that a DMM (especially one from the shack) needs to sample it's input and provide an average for the digital display so the voltage sag is far worse than you know. It takes a lot of juice to start a vehicle; starting it up and measuring after the batt has been sucked does not provide a picture of average power over time, which is what you're really concerned with. It's also a super-bad idea to mix batteries in a dual system... even the same battery of different age can sometimes be an issue.