Have a bad battery. Replace both? Or just bad one?

[retox1]

Went out to the garage to do a little preseason maintenance on the boat and found I had a dead battery. I Believe it's what people call the "house" battery as it runs my accessories and amps. So should I replace both of the batteries at the same time or just the bad one? They are both Optima blue tops,installed by the previous owner, but I would likely just swap in regular batteries as I am not a fan of Optimas. I've had a few in the past and found them to be nothing worthy of the price tag. Any thoughts?

[Ochrod]

I always have just replaced the one that goes bad. Never really thought to replace both just because one goes bad.

[chpthril]

A dead battery doesnt mean bad battery, so charge and test. beyond that, im not a fan of the optima AGMs. Cant beat the value of a good ol wet cell marine battery. If the batteries are isolated and used differently, no "need" to replace as a pair.

[retox1]

A dead battery doesnt mean bad battery, so charge and test. beyond that, im not a fan of the optima AGMs. Cant beat the value of a good ol wet cell marine battery. If the batteries are isolated and used differently, no "need" to replace as a pair.

Thanks, i did charge and load test it. I remember reading somewhere here that on some Tiges the ECM takes a voltage from both batteries and if they are arent the same or very close it can throw the boat into limp mode. I couldnt find the thread and had no idea if my RZ2 is like that.

[chpthril]

Although that wiring configuration was technically isolated to the 06 models with the EIDB, it has been found on some 07 models.