interstates are not very good & way overpriced... ive had 2 of them die in 5 years or less, not driven much & kept in climate controlled garages during peak of summer & all winter. i keep my batteries charged & do a few discharge cycles as well.

ive got close to 10 years on an autozone gold brand battery & 11+ years on an oreilys brand battery & its still going strong! all used in the same circumstances on 3 classic cars i own.

your treatment of the battery may not be helping & high heat or super cold when not kept fully charged will shorten the life a lot. buy a real battery charger & charge it for a few hours if it sits for more than a few weeks, & if you listen to teh radio for a long time charge it up afterwards. or buy a tender if it sits for a month or 2. driving it will charge the battery too. & if its not a maintenance free type, check the water level periodically & top off with distilled water.

ive heard of OEM toyota batteries lasting 10+ years... adjust your battery care procedure & you should be able to get a lot more than 5 years out of a battery.