Optima's are AGM batteries and as such, should only loose about 1% of full charge, even if you let it sit for a whole month. Without a battery isolation kit, what happens to one, will happen to the other.
On your daily drive, are you driving (or have your engine running) at least 1/2 hour? They could be chronically getting under charged by many patterns of bad behavior. Do you shut all electrical drains down before you turn off the key, head lights, park lamps, stereo, A/C, fan/blower? Do you have a high draw stereo system? Are leaving any draws on by accident, eg. dome lights, (though the '97 has the feature to shut down the dome(s), even if you leave a door open)?
My battery typically rests at about 12.4 volts after a sit overnight. I sometimes put a charger on, it set for 2 amps, overnight just to give it a little boost. I made a (+) lead on the big fuse block under the hood, so I don't have to pull the seat every time I want to give it a trickle charge. My red top lasted for 8 years. I now use a Duralast for a 1985 BMW 524td, 850 CCA.