You would probably be okay mixing battery brands, but. On a vehicle which uses two batterys it is generally suggested that you replace both batterys at once, just for the fact that one battery would be new and one old, and the older one would tend to pull the newer one down. I have a couple diesel tractors that take two batterys and it's just less hassle replacing both batterys with new at once. I would buy two of the less expensive, quality brand, same group size of course, and make sure they had atleast as many cold cranking amps as the originals. Just my suggestion.