Well it depends, at some point, the batteries will have to be charged back up is the alternator can not keep up with the demand.
Are you willing to ad an extra battery and charge the car up at home if needed? Or do you want to get a higher amperage alternator which will not require a second battery because it can maintain sufficient output?
Its up to you, I would find the maximum consumption of your electronics on the car, then compare that to the maximum output of the vehicle.
Voltage = Current * Resistance.
Watts = Voltage * current.
Find your wattage consumed on average of your things, find the wattage supplied.
Then go from there and compare how much time a second battery will allow you to go before you have to turn your toys off and let the car recharge.
Usually people add a second battery to help with the rapid current spikes that are required, and their alternator can keep up in between.
It is your choice.
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It is not necessary to buy an aftermarket HO alternator. Any higher output alternator can work, just look through the different manufacturers designs and find one with a case that is close enough to work with some modification. You can probably find a descent used one at the junk yard even. It is also possible to find a way to turn it on and wire it up to work with the vehicle, and to also change the pulley size and type as well as its fan blade so it works.
My 1996 Beretta Z26 now has a 140 Amp Alternator in addition to my 950 CCA battery.
I did consider a second battery, but I decided to get a higher capacity battery.
I did also consider an audio capacitor for my amp, but its not needed. I have a relatively weak amp only 300 Watts RMS output. I should have higher, but its sufficient for my needs as My bass is low, I don't like it really loud.
Here is a link to my alternator modification/findings if you want to read it, however it is specific to my vehicle:
Beretta.net • View topic - RENAMED & SOLVED - CS130 to CS144 Alternator upgrade (INFO)
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EDIT:
Okay I did some checking:
http://www.qualitypowerauto.com/catalog.php?item=470
I see the type of alternator your vehicle takes.
Here is the CS130 and CS144 GM alterantors that are a start:
http://www.google.com/imgres?q=CS144+alternator&um=1&hl=en&tbo=d&biw=1600&bih=756&tbm=isch&tbnid=WGQCc5LRi6dCYM:&imgrefurl=http://www.s10forum.com/forum/f106/bigger-alternator-upgrade-368983/&docid=kS5VJ77GvoLFTM&imgurl=http://www.syphoon.com/albums/album04/IMG_1844.sized.jpg&w=640&h=480&ei=O7XSUOAPhePSAcrTgaAE&zoom=1&iact=hc&vpx=350&vpy=267&dur=2462&hovh=194&hovw=259&tx=122&ty=80&sig=116747642432849148954&page=1&tbnh=135&tbnw=178&start=0&ndsp=34&ved=1t:429,r:10,s:0,i:117
These come in several different case mounting options, classified by vehicle. The CS130 alternator might be the right size if you get opposing mountings like your alternator has.
The CS144 alternator is physically larger, so maybe the offset mountings might work there.
Here is the 2 opposing mounting versions of the CS130 GM Alternator side by side:
http://www.google.com/imgres?q=CS130+alternator&start=73&um=1&hl=en&tbo=d&biw=1600&bih=756&tbm=isch&tbnid=YJJttmAaIClMFM:&imgrefurl=http://www.rx7club.com/1st-generation-specific-1979-1985-18/105-amp-alternator-swap-how-%2596-gm-cs130-504471/page4/&docid=7hjedU3rVlkq3M&imgurl=http://www.rx7club.com/attachments/1st-generation-specific-1979-1985-18/239433d1180047379-105-amp-alternator-swap-how-%252596-gm-cs130-dscf0005_edited-jpg&w=1029&h=687&ei=E7bSUKncMOW40gHjmoDoDQ&zoom=1&iact=hc&vpx=404&vpy=359&dur=1400&hovh=183&hovw=275&tx=143&ty=117&sig=116747642432849148954&page=3&tbnh=134&tbnw=224&ndsp=45&ved=1t:429,r:12,s:100,i:40
In the photo, you can see them, the one on the right looks close to your vehicles alternator, with the proper pulley and wiring, it can be made to work.
Selecting the proper bolts and maybe some washers to properly space it parallel so the belt goes on the pulley and it can be good to go.
Then you would have a 105 Amp max output as opposed to your current factory 80 amp max output.
If you need more, then the CS144 is an option with 140 Amp max output, just find one that fits, like I found the CS130 with a housing bracket close to yours.
And the best part is at the auto store or junk yard you can pay something like 80-140 dollars instead of lets say 400 dollars for a custom HO alternator, maybe 180 dollars, I'm optimistic.
Anyways, its a path you can chose to take. All I can tell you is on my 1996 Beretta the 105 Amps is just enough on the factory vehicle, so I had no choice but to install the 140 amp output alternator.
You only have 80 amps output. Your alternator is probably just enough to run that vehicle and all its electronics on at once, you add your audio system and you'll probably be lacking, and you'll probably need a larger alternator.
But do the math first, and see if you do, and then see what size you need so you don't have to mod it again if you ever have to go larger. Which you can still do if ever needed.
Just some info to throw out there. I hope this helps.
If you chose to modify your car for the higher output alternator, take the time to do it right and any future replacement alternators will bolt right on.
Also, you might have to either increase or decrease the belt size on your car, that however is going to be trial and error to what works best.
My car My belt needed to be an inch longer, but for now I am getting away with the same belt, it just has more tension on it as the pulley is a slight bit larger and the alternator is physically larger so the pulley is sticking away by a little bit.