what batteries should i use and why?

ive reached the part of my install that i need to figure out what batteries to use to power my amps.   i have a mmats 3500.1 and im pretty much lost as to where to even start.   please help.

Why do you want a battery? What size is your alternator? What input or output power (RMS Watts) are you designing for? ... and at what system voltage? Is the above for comps or regular use?

ill first apologize. i sent you a private message before you responded hoping that you would be the one to help me.   anyway im going to get a 300 amp alternator. im using a 12 volt system. my amplifier will be producing 3500 RMS. and im going to be mainly using it for regular use but also the occasional comp.    and i guess i dont know if i want a battery, i dont even know if i need one.   what are your thoughts?

No probs - no apologies. Besides, I gave a SHORT reply to your PM... (Yes Regulars, you can imagine how short that reply wasn't!) That PM reply probably made you aware of how many solutions there are to your question - even now that I have some answers... (LOL!) And yes - you read right - I did recommend a cap assuming certain conditions (yes - with an AGM next to the amp!). I know that seems to contradict my anti-cap stance elsewhere, but as I often write, there are some legitimate uses for a cap. (It's the other 98% I object to!) So battery or no? 3500W output suggests 3500/10 = 350A supply. (Estimate.) A 300A alternator may cover that assuming: - you aren't outputting 3500W all the time. - your battery(s) handles the alternator shortfall (whether at idle where the alt may only output 100A, or when the amp & car are "fully loaded" and you require 450A. - you don't mind the (say) ~2V voltage drop when the alternator can't supply the full load power. The alternator size also depends on your driving profile as well as load profile. IE - no good having a 500A alternator if you average 1,500RPM at 300A output when your total "average" load is 300A for the amp and 100A for the car & lights etc. You would have to charge the batteries at home to get thru the next day... Finally there is cost. If you want to spend heaps and often, I suggest you follow the advice of some audio forums - ie, use deep cycle AGMs (next to the amp), or any AGM in the engine bay... Best performance and overall cost will probably be with cranking AGMs next to the amp... The above effect battery sizing. But aside from those lovely complications, in general I would recommend a SECOND battery - and near the amp - for some basic reasons: 1: Independence. A battery isolator system (using relays or MOSFETs - not diodes) isolates the audio battery(s) from the cranking (main) battery. So if you forget to turn the amp off, you can still drive somewhere to tell someone about it. 2: Localised voltage drops. Although the distribution (wiring) from the alternator and main battery to the amp still have to handle the maximum load (ie, 3500W output plus audio battery recharge current), when the amp burps, most of the current should come from the audio battery (lower resistance to the amps, especially if AGM) hence a smaller voltage drop during that surge along the distribution cable AND at the amp. (And concentration of fat cables around the battery/amp only.) 3: Cheapest overall battery solution. You can keep your normal cranking battery. No need to replace it with a low-ESR AGM which then can't handle the cranking currents anyhow, and whose low-ESR is probably lost in the cabling to the amp... (Most OEM crankers are flooded/wet batteries. They won't self destruct as bad as AGMs do with high current surges. They are also cheaper.) Have I paraphrased my PM reply? BTW - diode type isolators cannot "share" the batteries. IE - the audio and its battery cannot draw from the main battery's capacity. Relay (and probably MOSFET) type isolators can. If you have a charge lamp, then the UIBI probably wins hands down. (That's simply where the charge lamp controls the isolator relay). Otherwise a voltage sensing isolator (aka smart or intelligent or (even more ha ha!) priority-charging isolators), but they need to be chosen carefully as burbs can trigger them to isolate, and then delays prevent reconnection for 15 or 60 seconds etc, so a burp every 14 seconds..... That's where I think IGN or ACC control is better...      I think the mmat literature suggests its amps can operate at 18V. You might then decide to boost the alternator to 18V (that's easy unless it is a D+ only type) and then drop that voltage for the rest of the vehicle and batteries. (18V x 300A = 5,400W, or probably about 4,300W amp output if the amp handles that, and all power goes to the amp. If total load is more than than 5400W, then the output voltage drops...) Different batteries suggest different voltages. I think Optima mentions 15.6V, but a normal float voltage for an AGM can be as low as ~13.2V as opposed to 13.8V for flooded cells. And I am wondering about UPS batteries. I confirmed yesterday a charging current of ~45A on my 38AH AGM (Yuasa UXH38-12) - that is simply not allowed!. That was after flattening to an OC voltage of ~11.4V (11.2V on dash voltmeter with ~2A max of load). UPS is High current & deep discharge requirements rolled into one, but at the expense of battery life - ie, they are not cyclic batteries. But after a few years as a main battery on different vehicles.... (To think I was once contemplating auto batteries as a alternative to expensive UPS batteries! An experiment I would still love to try, but hate to fail!)      Anyhow, some more food for thought. (Do you like eating currants?) (Yes, a re-volt-ing pun.) Too many solutions. Some depend on competition regs, others on how deep your pockets or partner are. Till next. PS - I wonder how those FloridaSPL standby AGMs are fairing? I hope they are in the engine bay.....