Dual batteries... should they match?

I am getting ready to add a second battery. I have done a search and have found what I was looking for in regards to wiring. What I couldn't find was any info about whether or not both batteries should match each other (brand, etc).

Optima's are not in my budget. I currently have an Interstate deep cycle that came with my boat. It is a year old. Do I need to make my second battery an indentical match to the first? If so, can the brands be different as long as the specs are the same? Will it matter that one battery is a year older than the other?

Also, I have a question about which batteries the amps/accesories should be wired to. I have decided to wire both batteries in parallel while using a Borg isolator relay. In this configuration should the postive from the amp/accessories go to battery #1 and the negative from the amp/accessories go to battery #2, just as the main battery cables will?

Thanks!

It's reccomended that both batteries are roughly the same age/make/model, ect. when run in parallel like you plan on doing. I've done it both ways same and differnt batteries and I've had no adverse effects from it. Theoretically what can happen is one battery is weaker than the other and charges differnetly than the other and over time they can act against each other and run themselves down. Do what I do and not worry about having the smae batteries , use a switch (manual) run everything off one battery, and use the second battery as just a backup. My perko switch is only ever on batt # 1 or off, I trickle charge my backup battery everytime it's in storage. The #2 battery is for starting/backup emergencies only.

That's not a bad idea. I am only runing two amps, so that may be enough.

Decisions, decisions, decisions.....

Or you can use this diagram from mikeski which is what I have done

Upload Boat_Battery_Diagram-276814[1].pdf (17.6 k)

I tried this yesterday, or something similar, hooking the batteries up in a circuit, like batery one has the positive lead and the negative leading to the positve of battery 2 then negative lead to ground, results were not good. I don't know but I have the feeling that like in a flash light you add up the volts when run like that. My Amp guage jumped up past 16 but the motor wouldn't even turn over. I quickly disconected it and went to the traditional positive to positive, negative to negative.

We went out again with same results as before, I have to be very careful to not run anything w/out the engine running or I might be flagging down somebody for a jump.

If somebody could help, I'm sick of not holding a charge. Two batteries both fairly new.

Rob,

I think that diagram is if you are using golf cart batteries. (6V) Put them in series, and you are back to 12V. You put 2 12V batteries in series, and ended up with 24V.

You just have to match the battery type. Like two wet cells, or two gels. Brand and size wont make a difference. If your wet cell is only 1 year old you should be fine just adding any other wet cell batt. Its fine to match a starting with a deep cycle also.

Richard:

If the batteries are ever going to be connected together via a battery switch then it is rather important that they are at least the same type of battery, that is, "flooded", "AGM" or "GEL".

It is better to have the batteries be the same age so that they will charge and discharge with similar characteristics but I wouldn't discard a year old battery in favor of getting two new ones. I recommend getting another flooded deep cycle battery (that's what your current battery is).

JTW: You should make a note on your wiring diagram that the two batteries in series are 6 volts each. I suspect Rob didn't understand that.

can you charge two different types of batteries with one alternator? I've got two optima blues and two golf cart batts. Yet to run down the golf cart batts, but trying to figure out how to get a charge to them to top them off while we're cruising