charge 2 batteries with isolator?

thank you.. I hae done alot of reseach on the battery combiner, and it seems to be what I need. I will try to get another Blue Optima //Battery for marine use, I just asked the question above because I have a Red Optima available now. the marine Blue optima is designed exactly like the RED, just hs two more post for marine applications, other wise the Optimas are the same, just Deep Cycle, or Starting

Great. Again, being marine, you probably do not have the UIBI (charge light) option - hence a smart isolator (ie, a low voltage isolator or high-voltage combiner - same thing). Nice to see a relatively high disconnect voltage (13.3V) - usually they are below 12.6-12.8V which means connected until slightly discharged; but such low voltages are chosen to prevent false-drop outs due to transient loads (brake lights, wipers) unless time delays cover it... But that's the switching problems we wrote of earlier.... Other than "marine hardening", the red or blue should not matter. And since Optimas are AGM, salt reaching the plates or acid is not an issue (bang!). But if "marine" also means different terminal metallurgy.... tresvatos - thanks for your reply. Thanks too for using an isolator. Although you want it anyhow for battery independence (a good idea for marine - it's a bit hard push-starting or finding a suitable slope, and it's somewhat more critical than for land vehicles!), I like it simply to extend battery life - especially after ONE of the batteries has failed (ie, and brings down the other one)! After an isolator, the only thing required for complete security & maintenance is a voltmeter. Backlit LCDs are probably best. I use a blue=LED in my car. (Voltmeters are one application where I think digital is good; 4-digit for accuracy BUT only 3-digit if on a visible console - eg, 14.2V on my dash instead of a flickering 14.23V etc. Otherwise an analog meter or expanded-scale meter (eg, 8-16V) is also good & has minimal draw - typically a few uA.) Whether 2 voltmeters or one switched voltmeter, I can check battery status and tell if one is failing.... I can also confirm suitable charging voltage (not too high, not too low...) Again tresvatos - thanks. And congratulations. Good design!

 I have decided to use a Battery combiner as pictured above between two Optima Batteries ( deep Cycle/starting )  Does anyone see a problem with the diagram..?  I need to find out a place to get the remote (ignition on ) pos wire to turn on my Stereo headunit..Should I get that wire from the right side BAtt that id conected to the Boat main on-off switch, so that it powers up when the boat main switch is turn to ON..? Thanks

The battery fuses should be at the battery terminals (diagrammatically - ie, protect ALL attached cables) not near the isolator. Where is the battery GND for charging? Not sure why you want he manual isolator - unless that is already there (as part of normal marine installations or safety procedures). I'd assume you'd want the HU to be powered from the manual switch's ON position (otherwise you risk draining the RHS battery). Are you voltage sensing for the isolator, or manual switching? If manual, with low-voltage protection?) And I guess cranker on the right with deep cycle on the left.... (or are these the "both" cranking and deep cycle batteries?)

Yes I found a smart isolator and I went ahead and decided to try that.  It cuts  circuit at 13.3 volts..  I am grounding to common engine ground, but forgot that in diagram..The headunit remote on should be to the reserve battery as well?? That makes sense, but I will need to put a switch to cut it on and off in order to provide power to the Head unit remote/ignition on whereas it would come on with main battery switch if I wired it to the master switch ON/OFF switch power pole.

Good to see a high switch-off smart isolator. Many are as low as 12.5 (and lower) which means 20% discharge. Few are above 13.0V. I would have assumed the HU remote was powered off the main battery, but with a smart isolator it make more sense to be off the reserve battery to avoid flattening the main.

Thanks! that is wat I will try until it poses an inconvienance.

Thank you ..I have found a used Optima battery that has 15.7 Amp-hours when loaded at about 20Amps and a rating of 10 Cold crank Amps after loaded for 15 seconds of trying to crank an engine simulator.  Would this Optima be worth the trouble to purchase, or should I opt for a brand new one? Thansk

That rating does not make sense. A 15AH battery is small and would never be charged at 20A (for long, or with valid warranty). They use 15AH (C20) batteries in emergency starter packs. I reckon they have more than 10CCA. From what I have seen, Kinetic are recommended over Optima in the states (or Deka down here in Aus). As to size, I don't recall any dimensioning info - what your load is, what reserve time you want etc. The general tip is do not discharge crankers below 20% and deep-cycle below 50% discharged (ie, 80% & 50% remaining).

Do these figures help explain a little better about the condition of this battery that I am contemplating purchasing? It  measures in at 15.7 Amp-hours when loaded at about 20Amps. Using an inverter with two 100W lightbulbs. It ran for about 45 minutes. A new battery would measure about 38Ahr for this test.

A Cold Cranking test using a carbon pile load, after the battery had discharged at least 6 amp hours. The CCA test consisted of a 350Amp load applied for 15 seconds. The voltage had to be at or above 9.6V at the end of the test. The CCA test passed with an end voltage of 10V.  Also, I tested it using a PulseTech 490PT Battery Conductance Analyzer and it passed.  Thanks for your help!  Greg