Be sure your mirror-mounted map lights aren't on. My tender wasn't keeping the (new) battery fully charged, ie, the green light didn't cycle. Car was under a cover. Next weekend I discovered one map light was on, probably hit it reaching for the garage door opener. Fortunately the tender was able to match the light draw so it didn't go down over the week.
Cooltech has a really nice kit that includes a Battery Tender Jr, but adds a connection point near the tow hook. It makes it real easy to connect the tender in the garage.