total system overhaul

If you want a "smart isolator" that only connects when charging, and you have a charge lamp, I have posted a few solutions - the best being the charge light (alternator D+ or L output) energises the isolation relay (grounded coil). It avoid the problems that expensive "smart isolators" have. Most alternator charge-lamps will drive a normal relay (~250mA) and probably up to 1A - but be careful - though they make "sink" one or several 250mA dash bulbs, they may not "source" the same current. (And some sink less to drive circuits or relays that power dash lights.)    If using BIG relays for 250A, 400A etc, then use the smaller L/D+ relay to energise its multi-Amp coil. Don't forget to fuse or circuit-break the battery - relay - battery interconnection at BOTH ends as close as possible to each battery. 2,000W will require at least 200A. Though there are bigger capacity batteries than yellow tops, you may want an AGM battery for its lower ESR - that depends on what the prime purpose of the battery is. If the battery internal and NOT in an externally vented enclosure, then the battery must (usually) be sealed - eg, AGM. And there are 14V battery options (for the extra 2 Volts - typically used by loud competitors and alternator-less racing vehicles (without CDI), but that depends on your amp quality (a good amp shouldn't care if it's 12V or 14V input). [ Is an amp output higher with a higher voltage, or "plenty of power" (at lower voltage)? ] If you are going for SPL, then avoid caps (most report higher SPLs with out them, hence their amp PSUs lack quality). And otherwise avoid caps anyhow (compared to an adjacent AGM battery, they usually make negligible if any difference). Many hereon reckon the Kinetic AGMs are good. Some reckon they are better than Optima - or rather - they last much longer.