batteries

first, I'm looking to replace my starting battery then, later on, add pine or two in the back. to replace my starter what battery would be best and same with the ones in the rear? I've looked at kinetik and optima mainly.

IMO stick to a normal battery for cranking - ie, flooded. From what I have read, Kinetik seems better than Optima. Down(-under) here I suggest Dekka - the Optimas are less reliable. But others have other opinions... And IMO, a battery isolator to isolate paralleled batteries when not in use. Google for "UIBI isolator", though there are also (more expensive) voltage-sensing isolators as well.

you don't mean like an acid battery for the starter do you?

Gels, AGM & flooded are all lead-acid batteries. For cranking, the flooded aka wets cells (as used for original OEM batteries) are the best for life-cycle (ie, last the longest). Plus IMO it's a bit self-defeating using a low ESR for the engine-bay cranker and audio when the audio (and other AGMs) are relatively a long way away - ie, via fuse and cable resistances. But that's a case of calculating the distribution resistance (ie, cable ohms/length x length) which usually boils down to the "extra" resistance of the +12V front- to rear interlink cable (since fuses and isolator and ground paths are usually the same for both setups, though the difference between the amp's "local" battery ground as opposed to remote battery ground can have a big effect - ie, amp-chassis to ground via (local) amp-chassis via cable to battery-, or amp-chassis via cable to bolt/car-chassis via cable to battery-; the remote battery being a much longer chassis else cable ground return.

well how well would a red top hold up for a starter then down the line paralleling with some kinetics or yellow tops? and i know its not best paraelling two different batteries but i have seen people do it before.

Like I said, why an AGM for the starter? If you think a redtop lasts longer than standard or other wet batteries, and it fiscally worth it, then it's up to you. But Optima is not my choice for AGM batteries, and from my readings, it seems Kinetic is a better choice stateside. [Here in Aus, Deka has been recommended to me. I would use Yuasa over Optima here - bigger for cheaper, and far more reliable - certainly for cranking (I am using a Yuasa UXH-38AH).] As for rears, it depends on the use. For audio surges, I would use cranking batteries. Deep-cycle for lesser current surges and if a greater depth of discharge. Paralleling of unmatched batteries is ok of they are being used (charged or loaded). It is only if left too long in parallel whereby a failure means that both will fail (and possibly hazardously if AGM - eg, thermal runaway). But fitting some form of isolation is a small incremental cost, whether manual isolating switch(es), relay(s) or even a UIBI or voltage-sensing isolator.    Usually people fit an auto-isolator at least to separate the main cranking battery (to ensure enough reserves to crank & start). Further isolation depends on the load(s). EG - if 3 batteries for 3 different loads (main; fridges or PCs; audio or other), then the "main" isolator (UIBI or voltage-sensing) is used only to energise the 2 isolating relays for the 2nd & 3rd battery. Hence all 3 batteries are independent if the vehicle is not charging. If it's for big audio (ie, a main battery and whatever paralleled audio batteries), then it's usually the normal isolation from the main battery (UIBI etc) with manually energised relays or switches or removable links between the secondary batteries when they are not in use.

well the only purpose i need the for is a big audio system. so would my best bet be to get a battery for the front then have an isolator between the front and the back and parallel up my back ones?

As to the big audio system, so you know that the distribution resistance between the from battery and the amp is negligible compared to the ESR reduction of a front (cranking) AGM?     And you know otherwise that - else consider it worthwhile if - cranking means replacement of the front cranking battery more often? As to the above AND your last question, I thought my opinion was clear in my above reply(s)?    (HINT - leave the front battery alone!!!!)

sorry, i guess i misread. But, correct if I'm wrong, it is best to use a wet cell for cranking, and then use an isolator and have deep cycles in the rear for the audio system?

Yes. But... Probably cranking (AGMs) for audio IF it is the big audio thumps you are trying to accommodate. If they will be discharged (when not charging etc), then deep cycle. Why? Deep cycles are not for heavy drains. High-current batteries (crankers) are not for deep discharge. The isolator (like a UIBI, else voltage sensing aka "smart" isolators) is twofold: (1) independence from the cranker when not charging so you have a battery reserve for cranking & starting, & (2) to NOT parallel batteries when not being used (ie, not charging or supplying a load) because - given enough time - a bad battery will discharge and ruin the other parallel battery(s). Also to prevent possible thermal-runaway with AGM batteries (but that can happen when charging; battery condition (or temperature) must be monitored at suitable intervals). Whilst the UIBI or smart "auto" isolator is used to isolate the aux from main battery, it can be used to isolate the aux parallel batteries (use the UIBI/smart as a "master" that only switches the isolating relays) though generally for audio etc any secondary paralleled batteries will have a manual bypass, else be isolated from each other manually when left for longer periods (manual switches or disconnecting at terminals etc). To explain my wet-cell cranking madness: Though AGMs can supply higher currents, it does not mean they like it. (Analogy(?): Maybe your engine can supply more power above its red-line?) Wet-cells are less prone to damage from high-current loads. That is largely due to their higher internal resistance, but other "wet" factors may also relate. You can get a bigger AGM so that its "high current" is less in proportion to its AH capacity, but the same logic still applies to the equivalent sized wet cell. Note that there are two basic forms of battery construction - high-current with more plates that are thereby thinner (to fit in the given size), and deep discharge with fewer but thicker plates. And the lower the discharge (and recharge) current(s), the better for the battery. If AGM batteries are cheap compared to wet cells, then why not use them for cranking? (AGMs are generally only used for crankers when vehicles spend long times between starts - eg, collectors & vintage cars etc, else for high-current starters.) But when eg Optimas retail here for ~$500 compared to ~$100-$125 for equivalent or bigger wet cell crankers, it becomes an expensive cranking option. It is usually far cheaper long term to keep the original cranker and add the AGM next to the amp (where it should be, of course!) - not to mention the redundancy benefits. So, there are 3 main competing issues: - AGM versus wet cell - cranking versus deep cycle - next to the amp versus remote (eg, the engine bay). The "correct" solution depends on the aim or intention, the budget, and life-cycle costs.    Life-cycle is normally most effected by temperature (each 10°C increase halves battery life), but the number of cycles, the depth of discharge, and load (and recharge) currents have their effect.