Team MightyBoy

If i'm to install an auxillary battery of that same capacity as a stock battery in my hatch then would the stock alternator be able to charge both batteries? I want to fit an aux batt to power an amp and few extra lights.

Thanks guys.

Simple mathematics. Add up the watts draw of the equipment you wish to fit and divide by 12. That will give you the amps required.
The Mighty Boy alternator is good for 35 amps I think.
For safety sake you need to allow for losses etc., say 5 amps, so your total draw cnnot be more than 30 amps.
Remember the ignition system and lights and fan in the car already draw substantial current I suggest you cannot go much over about 10 or 12 amps or 120 to 14 watts.

MightyBoy alternator makes 25A, Hatch alternator (the one with fins on the pulley) makes 30A.

Why not just install a higher CCA battery in place of the one you have? Something like a deep cycle Odyssey or similar?

It's not hard to get plenty extra CCA under your bonnet without having to go to something really expensive either. What do those little stock batteries push out? Couldn't be over 200CCA, surely!?

You can fit a 280CCA Bosch / Century battery under the bonnet in the standard battery cradle easily. I did!

Crank, bear in mind that a second battery will only allow you to get away with running a lot of draw for slightly longer periods than with a single battery. In all likelihood, the stock alternator still won't be able to keep up with the amount of current draw during running periods, and you'll have to allow substantially longer periods of minimal draw on the system to achieve full charge in both batteries after running them low.

Instead of adding another extra batt i went for a higher capacity batt which comes in the Esteem (Swift). It's a Bosch Silver 38. The electrics are running better now. Maybe i'll fit a Estem (swift) alternator later, it has more amp rating 55 or 60 (can't remember).

Thanks fellas.

I had a hatch with a 330CCA battery in it... Never had a drama running bigger headlights, stereo and amp...

with a little Modification to the mounting bracket i managed to get a 380CC Battery under the bonnet of my Hatch, a little tight but it fits, Put this in when it used to be my daily driver and had 3x more stereo value than the car..... what can i say everyone knew the car cos it was all stereo and no car!!

Hewball

arnt u ment to figure out your rms rating for your amp/s.....
add these together and multiply by 2
the figure u get should be your total imput draw in watts
divide the wattage draw by 13 ( the average vehicle supply voltage)
the figure u have should be the current draw in amps.

dunno if thats right but thats what ive bin told