2nd battery w/o isolator

What's the word on using a 2nd battery without an isolator. This is going to cause charging headaches, no? If not an all-out voltage drop?

adding a battery is probably not going to help your problem.  infact it my cause more problems.  power problems are easy to fix.  BUY AN ALTERNATOR that can supply the proper power for your system and your car.  Under normal circumstances a vehichle uses 40 - 50 amps to do its thing.  the rest of the power from the alternator runs your accessories suck as the stereo.  adding an extra battery to your car without getting a bigger or dual alternator gives you more power storage but you still have the same amount of power being supplied.  it may help in the short term but it will cause extra strain on your alternator and eventually damage it or cause it to fail completely.  Stiffening capacitors have the same efect but they release power much faster than batteries do.  they charge almost instantly as well.  a 1 farad capacitor will get you less than 3 seconds of added power before it is drained and your battery starts to drain!  just think of it like this, if you have 2 batteries your alternator has to work twice as hard to keep them both charged.  as far as an isolator is concerned, if you get a good one you should be ok.  the cheaper isolators will cause a voltage drop.  the reason you would use an isolator is to protect the cars factory electrical system.  an extra battery will not damage these components.  The best way to solve a power problem is to get a high output alternator.  Once again, don't look for a cheap one.  a true high output alternator will run from $400 and up.  Remember you get what you pay for.  Stinger has good units but they are very expensive.  I reccoment Ohio Generators.  I have a 200amp in my truck and no power issues at all.  I hope this helps.Jared Nixon - A.K.A Jsmoke

3rd Coast Customs

Lake Charles, Louisiana

Plenty of good info in there Jared but not what I was asking. I'm curious what happens when two batteries are used parallel w/o an isolator but with accessories on each. Is there a voltage drop or other penalty when a single alt tries to charge/maintain across two batteries at once? What about 2+ batteries paralleled in a bank, meaning not separated across the car and no accessories pulling from each? In theory they're acting as one battery with multiple cores - does that need an isolator? I'm well aware of the benefits of an HO alt, this is more of a theoretical question. Thanks.

Whoa - how did that happen??

lmao, happens to me alot also. but i usually have just 2 posts xDtwo 12" cadence TXW-12S, cadence TXA-3002 amplifier, 1990 toyota celica system 10 speakers

boulderguy wrote: Whoa - how did that happen??

I fixed it.  Sometimes the server gets a little wacky.

If you place two batteries in parallel you in effect create one larger battery.  It doesn't matter where they are physically located, it matters how they are electrically connected.  Yes, it can place more load on the alternator since it can require twice the current to recharge, but if your voltage regulator is functioning properly it's more likely just to take longer to recharge.  A larger battery capacity will also mean it will take longer for the battery voltage to droop when load is being placed on them.  This is true whether it's placing two or ten batteries in parallel or whether it's simply installing a single battery with more capacity.  Batteries in parallel = same volatage as one, but with twice the current capacity.

The purpose of a battery isolator is to separate the normal engine battery from a second battery system intended for running auxiliary loads - whether the load is an audio system, a winch, a compressor, etc.  The idea is so you can operate these loads independent of the vehicle's normal electrical system, but then connect the second system to the alternator for recharging when necessary.

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I get it, thanks. I had it fixed in my head that you didn't want the alt charging two batteries at once, as if that would dilute voltage. Thinking about it more & I realize it's the current that gets divided, not the voltage. Thanks all. I'll try to relax with the "post reply" button.