factory dual battery

[86k20mudddigger]

i got a 86 k20 with the factory setup for the dual battery. i hooked everything up they way it looks like it should be ran. and am getting no charge. i called the guy at the local parts house and asked if my truck had an factory isolater and he said no but it has a "Battery Switch aka Battery selonyid" spent the 30 bucks put a new one it and still no charge. im getting 14 volts to the right side battery (starter batter) and only 12 out of the other side of the switch. i guess my question is does this so called switch charge the first and the click over to the second? anything on this would help so i dont have to keep a trickle charger on my second battery now that i ran my headlights off of it.

[tucsonjwt]

I don't know what set up you have, but I have had the isolator, solenoid, and dual start battery setup. Unless you need to have the second battery run RV equipment, I would stick with just wiring the two batteries together. That gives you two "start batteries" like a diesel would have.
I have two batteries because my 454 starts hard when hot and the two batteries help overcome that. I believe both batteries get charged at the same time, but I noticed my second battery seems to get less of a charge. It does take a lot longer to charge two batteries instead of one battery. I do have a 140 amp aftermarket alternator. Of course, when one battery goes dead they are both dead. With an isolator, the second battery won't get charged unless the primary battery is fully charged.
I found that isolators don't last very long before they crap out, and I did not see the point of a solenoid unless you manually switch it from inside the cab, which was the setup I had at one time - just a pain to fiddle with when starting.

[86k20mudddigger]

and have you ever ran into any probleams or no? and you said you manualy have to switch the battery switch to get the second to start charging? and im running a aftermarket alternator but im having a brain fart and cant remember for the life of me what amp it is. but i do know for a fact it is higher than stock.

[tucsonjwt]

With my current set up - just two batteries wired together - no problems. However, I don't drive enough to keep the batteries charged - maybe once every two weeks, on average, so the batteries eventually discharge due to lack of alternator charging. This is not the fault of having dual batteries. When I put the trickle charger on the batteries, I noticed the secondary battery had a lower charge than the primary battery. I am no auto electrician, but I think the additional cable length to the secondary battery results in some voltage drop which slightly reduces charging to the secondary battery.
With the isolator setup, the isolator only lasted about a year or so before the diode(s) failed. I read that you can get higher quality isolators which are supposed to last longer (maybe $100+), but I don't know about the warranty on those. The secondary (RV) battery did keep its charge, but that is the only advantage I can see to having an isolator.
With the solenoid setup, the mechanic who installed it said both batteries will charge at the same time when the engine is running, but when the engine is off the secondary battery is disconnected from the primary battery. I would push the button he installed when starting the truck to activate the solenoid to connect the two batteries together to give me more amps to start the 454. I am sure you could wire the solenoid to the start wire to accomplish the same thing.
Bottom line, with any set up, your secondary battery will always have less charge than the primary battery, unless you drive a lot (driven enough to put out enough amps long enough to charge both batteries - twice as long as enough to charge one battery.) Even with just two batteries wired together, the secondary battery seems to have less charge (my theory is voltage drop, as described above.)
I don't know why your headlights should be running only off the secondary battery. They should be wired through the normal wiring harness to the primary battery.

[86k20mudddigger]

Th reason I have my headlights off the second battery is because I got the HD headlight harness from lmc tO run a HID setup. My buddy keep saying I should run a second battery because I have so much other things running. Lights stero and plans to do onboard air comp. I guess i will try connecting the two batteries together. Do I need to ground the two batteries together or can I use two separate grounds
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[lindstromjd]

Use 2 separate grounds. Works better. Electricity is only as good as the ground you have it hooked up to. I have duals in my diesel, and run a power wire and ground wire to my secondary battery, but also have a separate ground hooked up to the secondary. So from primary battery; power to starter, power to secondary, ground to ground, ground to secondary, and secondary ground to ground. Kind of like piggy-backing them off each other.

[86k20mudddigger]

Thanks for the help guys
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[tucsonjwt]

I have long positive and negative cables running from the secondary battery to the primary battery - that's it. Another negative cable from secondary battery to vehicle ground won't hurt. You can also just run a negative cable from the secondary battery to vehicle ground, but the traditional way is to connect both sets of battery terminals together. If you don't use an isolator or solenoid, you can run the cables through holes in the core support and suspend them with cable ties under the upper grille support/core support to keep them out of sight and away from damage. I used large rubber grommets in the core support holes to prevent chafing of the battery cable insulation.
Running your headlights, and any other extra accessories, off a secondary battery would have the effect of saving your primary battery for starting and normal loads only. This would avoid having a dead start battery from excessive loads. See my comments on using an isolator above.
Two batteries, no matter how you hook them up, won't do you much good unless you drive enough to charge them up. If your truck is a daily driver with maybe 20-30 miles driven per day, both batteries will probably stay charged. If you drive 5 miles once every two weeks like me, then you will have to trickle charge your batteries every couple of months to keep them fully charged. This is true of any vehicle, regardless of the number of batteries. People who own classic vehicles and rarely drive them usually keep them on a slight trickle charger all the time. I will probably end up doing that with my truck.

[86k20mudddigger]

Unfortunately at 6.5 mpg this is my daily driver. But I'll give the double cable route a try before I go spend tons of money on a isolater
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[tucsonjwt]

I don't know what kind of rig you have, but 6.5 mpg sounds like a big monster mudder with modified engine. Otherwise, 10 mpg city is possible, maybe more.

[86k20mudddigger]

Lol it's a monster all right. I pass everything but the gas station
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