Now if I wanted to have 2 batteries in a car. What would be the best way to do it? Running them in series or parallel? Would they have to be the same? Any down sides to doing this? Will doing this help out my run time for the stereo when the car is off?

Thanks

I used an isolator for my duals. A few people I talked with mentioned doing them in series and whatnot, but everyone else told me an isolator was safest way to go, so thats what i did.

Its just roughed in right now in these pics, but it'll give you an idea anyway Main battery still mounts in stock location.

If you wire them in series and the connect them to the car. WELL, let's just say you ARE IN FOR a SUPRISE. 12 volts in series with 12 volts is 24 volts. To increase you current capacity wire the two batteries in parallel. BUT if one is weak, again beware.

An isolator is good advise...

I guess the series idea is bad . Whats the worst that can happen if they are in parallel?

quote Originally posted by Master_Sushi: I guess the series idea is bad . Whats the worst that can happen if they are in parallel?

Hm .. but just think how fast it'd start on 24 volts! <smirk>

Theoretically you should be able to wire a hundred batteries in parallel and just have a hundred times the amps available at 12 volts.

Vic

Ooops... in my first reply i mentioned series.... mindscapes right, thats 24v! I meant parallel, but was told negative effects of that as well...something about the batteries possibly discharging into each other or something like that. Also the batteries had to be of same make/model/production sequence in order for it to work right.
Either way, same end result, almost everyone said isolator was the way to go...

For negative effects however, an isolator will suck up about 0.6 volts from your output if memory serves, not that that is even noticeable in mine, but it was mentioned in the instruction set for the isolator, so i guess it could cause problems in certain applications.

The best thing is to put two identical 6 volt batteries in series, that doubles your current capacity, but has no bad effects.

It would be like taking a 6-cell 12 volt battery and cutting it in half, but since each cell is twice as big in a 6 volt battery, you have double the reserve capacity.

Just remember that all the grounds have to come off the ground on one, and all the hots off the hot on the other, with nothing but the heavy cable connecting the two together.

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Gerald Storvik

http://www.8shark.com/

Parallel with an isolator is your best bet. You could probably put them side by side under the spare too.
Reminds me of a '52 Pontiac Chieftain I had that I converted from 6V to 12V. I was too lazy to do anything about the original 6V starter so I just ran it off 12V. The car still starts fine after 10 years, boy does that starter spin quick tho...

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Bob Cardone
Suncoast Fieros

'85 2M6 SE Targa

Definitely in parallel....although I'm not sure why the isolator. I ran them this way in my 68 Firebird for years with no problem.

phil

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GTDude
25 years GM experience

I just set up the dual battery system in my fiero. Seems to be working great so far!

Ran two 650 crank amp batteries in parallel. Used heavy jumper cable wire to run them into the trunk. I connected and wired them up with all new hardware.

The car cranks over MUCH faster, and I have noticed allot more power when the engine isn't running.

Next fiero I get I am for sure going to do this. I will probably put the batteries up front though. It probably dosen't help to have 40+ pounds in the trunk.