what is my secondary battery suppose to read while car is running

[ManzKea 152]

Hey guys quick question. I got a dodge challenger and I upgraded my starter battery to a kinetik hc2400 and then I recently added a hc1800 as a secondary battery. I recently brought a dmm to mess with and check the Ohms of some subs I had lying around. Then decided to check my voltage . So both says it rests at 12.8 then I started my car and the main battery read 13.78 or so and I checked my secondary battery and it read 12.8 like nothing happened.

This is the first time I've ever checked my secondary battery, I've had a dual battery set up in my altima. And I had the LCD volt reader and my secondary battery was in my spare tire area under my sub so I never really bothered. Is it suppose to jump up like the main battery? I brought the hc1800 off of Craig's list and the guy said he had it sitting on a tickle charger. I had it for about a month now so idk if this is normal or not. Thanks for any info guys

[Triticum Agricolam 15]

How do you have your second battery wired in?

 

The 13.78 volts you are measuring is what your alternator is putting out, you should be reading that everywhere.  

 

Personally I'd be pretty wary of used batteries unless I really knew the history on them.

[ManzKea 152]

That's what a I was thinking! And I have it wired in parallel . So I should switch the thing. If that's the case I can get a good deal on an optima but I know it's frowned upon to mix batteries

[ManzKea 152]

Could I possibly charge it or something?

[hdrox88 142]

I would suspect a bad connection somewhere. Go over all connections and also check fuses and holders.

[Triticum Agricolam 15]

Lets try to isolate the problem a bit.  Unplug the negative wire from your second battery, start your car and then measure the voltage across the negative cable to the positive cable.  You should get the same voltage as what you get at your primary battery, if you don't something is wrong with your wiring.  If you do get the same voltage you can try taking out the second battery and charging it up.

 

I am not a car electrical expert but I think that AGM batteries use a different float voltage than regular wet lead-acid batteries.  I also know that some trickle chargers will over charge and ruin a batter if they are left on it too long.  I'm not 100% sure on either one of those so hopefully someone more knowledgeable will chime in too.

[ManzKea 152]

Lets try to isolate the problem a bit.  Unplug the negative wire from your second battery, start your car and then measure the voltage across the negative cable to the positive cable.  You should get the same voltage as what you get at your primary battery, if you don't something is wrong with your wiring.  If you do get the same voltage you can try taking out the second battery and charging it up.

 

I am not a car electrical expert but I think that AGM batteries use a different float voltage than regular wet lead-acid batteries.  I also know that some trickle chargers will over charge and ruin a batter if they are left on it too long.  I'm not 100% sure on either one of those so hopefully someone more knowledgeable will chime in too.

Alright that sounds like a great suggestion. I'll try that tomorrow . All connections should be good. They are litteraly less than 20" away.

What also became a concern is what my amps are seeing volt wise. Since its coming off the secondary battery, does that mean this whole time my amps have been seeing 12.8 volts? Lol

[Triticum Agricolam 15]

...What also became a concern is what my amps are seeing volt wise. Since its coming off the secondary battery, does that mean this whole time my amps have been seeing 12.8 volts? Lol

 

I'd measure the voltage at your amp, that will answer your questions really quick.

[95Honda 486]

They should read the exact same voltage if they are wired in parallel, assuming you have sufficient gauge wire to not let much voltage drop.  Something is wrong.

[Randal Johnson 544]

Do you have a distribution block between batteries ??

[ManzKea 152]

No distribution blog k. Just positive to positive negative to negative. With a fuse between the two. 0 gauge wire. And I connect my sub and 4channel amps direct to the battery

[puscifer2 27]

Did the fuse blow?

[khinds94 17]

I had same problem it was fuse between primary and second battery

[Frostedflakejake 148]

They should read the exact same voltage if they are wired in parallel, assuming you have sufficient gauge wire to not let much voltage drop.  Something is wrong.

 

This. The batteries are not truly connected in parallel, at least not when the vehicle is running. Batteries in parallel must satisfy Kirchhoff's voltage law which in this instance requires the two batteries to have the same voltage. 

 

I would first do as khinds94 suggested and check the in-line fuse (if you have one) between the secondary battery and whatever source it's connected to. If that's not it there is an issue with how the secondary battery is connected. 

[altoncustomtech 773]

Do you know if there's a battery isolator being used? If it's not a good one and connected correctly there could easily be a .7vdc or more drop between the batteries.

Otherwise I agree with the others and there has to be a connection issue somewhere.

[Frostedflakejake 148]

Do you know if there's a battery isolator being used? If it's not a good one and connected correctly there could easily be a .7vdc or more drop between the batteries. 

Otherwise I agree with the others and there has to be a connection issue somewhere. 

 

Good point. My previous statement is true for a lose less system which is of course impossible in the real world. However I still doubt losses are what's accounting for the voltage difference. 

[ManzKea 152]

Alright guys thanks for the suggestions. I will look into the fuse. I am not using am isolated. Just running it in parallel.

Wouldn't the battery slowly drain if its not connected to the main battery. I've had it in my car for a month or so

[ManzKea 152]

Thanks so much guys. It actually was the fuse! I guess I overlooked it because I have those with the led lights that suppose to light up when blown. I swapped it and sure enough second battery shot up to 13.08 a little less than the main battery but I'll take it. Especially with my taramps 5k

[Frostedflakejake 148]

Thanks so much guys. It actually was the fuse! I guess I overlooked it because I have those with the led lights that suppose to light up when blown. I swapped it and sure enough second battery shot up to 13.08 a little less than the main battery but I'll take it. Especially with my taramps 5k 

 

Hm. Still lower than I expected. I guess the difference could be composed of difference in internal resistances. 

 

Just for clarification, with the batteries hooked in parallel both will be feeding your amplifier. 

[ManzKea 152]

Thanks so much guys. It actually was the fuse! I guess I overlooked it because I have those with the led lights that suppose to light up when blown. I swapped it and sure enough second battery shot up to 13.08 a little less than the main battery but I'll take it. Especially with my taramps 5k

Hm. Still lower than I expected. I guess the difference could be composed of difference in internal resistances. 

 

Just for clarification, with the batteries hooked in parallel both will be feeding your amplifier.

I guess so. I'm not too certain. It's wired in parallel, and my amp power and negative wires go directly to the secondary battery. No isolators to separate the two batteries. Just a fuse on the positive wire between the two batteries

[ManzKea 152]

I did not run a 0 gauge wire from the alt to the main battery. I just upgraded the ground wire, and the accessory power wire. Reason being, my main battery is in the trunk, and the alt is up front. I need to run the wire under the car, so I'll save that job for later

[Frostedflakejake 148]

 I need to run the wire under the car, so I'll save that job for later 

 

Yes with that much power I couldn't strongly recommend that enough.

Have you tried to see if you can fit 1/0 gauge in the wire runs of your car? I can easily fit 1/0 gauge with room to spare in mine.

Wire runs are a much less hostile environment than the underside of the vehicle.   

[ManzKea 152]

What kind of car do you have? And I know I know that's like one of the main parts of a big 3 but I was lazy

[Frostedflakejake 148]

What kind of car do you have?

 

2004 Ford Explorer

[ManzKea 152]

Well idk where my wires go. Lol it just comes out this spot in the car, and it's like 8gauge or so. Plus id have to drill through the passenger fire wall and what not. It would be easier I believe to run it under the car. Tuck it somewhere out of direct exposure