Couple things that haven't been mentioned so far-

If you alt is charging with correct voltage, what would getting a high output alternator do? Isn't a high output alternator for when you're running so much stuff it can't properly charge? I just did the Bosch 115 alt upgrade myself, but my alternator was dead.

Another suggestion not mentioned- a turbo timer. Whether you have a turbo or not, you could easily install a turbo timer (prices vary to very cheap to very expensive). This will let you set almost any set amount of time to leave the car on after you have pulled the key. So, you could drive for 5 minutes and then let it idle in the parking lot unattended for 10+ minutes - however long you so desired. This might be healthier for your car as well as your battery.

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Greg
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85' 300TD
03' Honda S2000