Battery replacement

[AstroDiver]

One of my batteries is the original. I also have a back up that is bigger. Both are standard wet cell types.
The original shows 12.5+ volts but won't crank the outboard.
If I replace this battery with an AMG type will there be a problem with the other battery?

Both are on one of the battery switches, "OFF 1 BOTH 2" type.

Since they are rather expensive, I was thinking of replacing the second battery when it decides to give it up. I was looking at Odyssey brand, PC1200 unit to replace my cranking battery. Both are located in the aft center compartment. My boat has a Suzuki 115.

I will be pulling both of these batteries out for servicing...checking water levels, etc.

Thanks for any pointers.

[rodman1472]

Astro Diver,
Check with your battery supplier, but even better a marine outfitter. My understanding is that both batteries must be of the same type, otherwise there could be problems with one or the other.