Car audio upgrade

I'm concerned for your hearing, and for the irritation of your neighbors.

You are correct that it will slowly drain the battery, but not because the charging system can't keep up. Honda uses an unnecessarily-complicated charging system in which everything that uses current gets "polled", or added to a list, then that list is used to calculate the needs of the electrical system. The generator is directed to develop exactly the amount of current needed, and no more. An aftermarket radio is not included on that list so its needs are not included in that calculation. Some people say they've never had a problem, but the common symptom is the battery has to be charged every few weeks.

One of my best friends is totally deaf, and I see what limitations he has in his daily activities. A few former coworkers now have severe hearing loss and they're in their early 40's. The government sees fit to stick their noses in the lives of cigarette smokers, but they don't care about you losing your hearing. I urge you to reconsider what you're trying to do.