"The main need for the Battery Tender is because someone installed an aftermarket sound system and an alarm. Which of course drain the battery when the car is turned off."
All the more reason to get a fresh battery in there and remove that variable from the equation. Sounds like you should likely go with the Group 49 option. I had a Porsche branded battery go bad in less than 18 months and it wasn't saddled with all the extra stuff it too was either on a tender or disconnected during that time.
Yank all that aftermarket crap as soon as practicable (I should probably put a viewer discretion warning on these pics)...
