Dual Batteries

There is a problem with "running a charging wire" to the second battery.
The knife switch doesn't isolate the battery. The Alternator charge wire is connected to the main accesory supply (fuse box) so you would still need to have a high power (same amp as your alternator) diode to isolate the second battery from the rest of the vehicle. Since that is what the Isolator does you can see the problem with adding a knife switch to the circuit. By the way, a knife switch that could handle cranking current (200 - 300 peak amps) would be very large.
If you want to protect your cranking battery from the power draw of other things (like a stereo amp) then use an isolator. If you need cranking capacity then use a dual system connected in parallel.
Yes, you can buy the solenoid system. Then you just have to switch the battery off when you want to protect it and remember to switch it back on to charge.

 

Check out Painless Performance part number 40102

 

Yeah. I was looking at solenoids earlier. Looks like I'm going that route.

 

Well, since you've been around mechanics forever, I'm sure your aware that they sell knife switches that attach to the top post of a battery, for the very reason of running dual batteries, so they aren't hard to find.

I've been told you can run a seperate wire from the back of the alternator to the second battery, so it charges off the alternator but isn't connected thru the car itself. I'm not sure of this I'm wondering if you could do this or not...

I do agree the diode/solenoid/isolator would be the best thing to do.

BTW, not all isolators use diodes anymore, that's the "old" versions.

Also, I find there no need to run dual batteries just for cranking amperage in itself, just buy a higher cranking capacity battery if that is the ONLY reason your wanting to run dual batteries.

 

there is only one charge post on the back of an alt. so if you ran a wire from that post to each bat you are effectively connecting the bats. in parellel.

 

That's what I was thinking but wanted to make sure.

I read where you can use a toggle switch inline the second wire, but that seems ghetto. lol

 

i would sugest just geting a really high qualilty batery. i am not experienced with really cold weather living in so cal but i would figure a good batery like a optima should meet all your needs.

 

Ost places that get really cold weather use battery and block heaters to make the engine easier to start up after sitting all night. The reason for this is that as a battery gets colder, the chemical process that produces electrical amps slows down. Lead acid batteries are extremely sensitive to this and while some batteries can work almost as well at temperatures down to -70F lead acid batteries quit working for the most part at those temps. At 0F a lead acid battery only produces about half the power it does at 80F, so if you live in the part of the country where temps often drop below freezing it is important to keep the battery warm. A battery works under normal conditions long after it won't start a warm car when it gets into the twenties (as folks here in the Seattle area have found out over the last couple of days). A battery heater does no good unless it is plugged in - if you have to work eight hours you may need the extra power of a second battery by the end of a cold day at work.
For the rest of us we can go along in total blis until cold weather hits and we find our batteries lacking.

 

Not trying to argue, but wouldn't buying say a 1200 cranking amp battery, be the same as running two 600 cranking amp batteries..

I know the cold cranking amps are lower than that, but say they are 600 a piece on the 1200, and 300 on the 600... it'd still be more power in the 1200 battery right?

I could see running 2 of the bigger batteries, but someone's arguement earlier was to just get a bigger battery if all you wanted was the cranking amps only.

So would the bigger battery alone be better/worse/same than the 2 smaller ones?

 

I'll add in the fact that a 1200 amp battery will have a shorter lifespan than a 600 amp battery.
It's better to try and match your cca needs than go for complete and utter overkill.
So 2 smaller 600 amp battery's may have another year in them versus a single 1200 amp battery.

 

Curious as how you came up w/ that answer?

 

Observation.
I used to work at a boating store that sold batteries.

 

Oh, was just curious.

I had a 1100 amp battery that lasted me about 5 years. It was a replacement for a 800 that only lasted 3.

Guess I got lucky.

 

I'm glad this started up such a big conversation. Some of these questions I didn't even think of. Thanks again, guys.

 

I've thought about that. The main reason i want two is just to have a dedicated accessory battery. But the main one would definitely be an optima. And thank god for that weather. It's 17 degrees here with a wind chill of about 9 degrees.