im buying an SVR33-12 batterie and they are no longer produced. i want to buy another of the SVR28-12 which has the EXACT same specs as the SVR33-12 except its 5lbs lighter, so would i be able to wire the 28 and 33 together as 2nd and 3rd batteries since they have the same specs just different weight and shape ??
I wouldn't. If it's 5lbs lighter, something is different inside....... it is the resistance of the battery that matters when wiring in parallel. No two batteries will ever have the exact same resistance, which is why it's not even good to wire identical batteries in parallel for a daily system. If they are identical, it will be close though, and probably not cause a problem if you don't let the car sit for a long time.
In this case I would bet that they are not identical inside.
^^^^ You could do that, or isolate the bank of batteries from the front battery, either method works.
When designing a system, I do not even wire more than one of the exact same battery together, because I never know if somebody may let the car sit for a long time without being driven. Like I said, batteries wired in parallel will slowly drain each other. If you drive you car regularly it's not a problem though, since the alternator recharges them. If you let the car sit for several weeks or months and then went to start it, you most likely would have a bank of dead batteries, or low voltage at least.