Need another battery
#2
Use a relay. They don't draw juice like an isolator would. More power for your tunes. 
http://shop.pkys.com/automaticchargingrelays.aspx

http://shop.pkys.com/automaticchargingrelays.aspx
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Some people are like Slinkies - Not really good for anything, but they
bring a smile to your face when pushed down the stairs.
Some people are like Slinkies - Not really good for anything, but they
bring a smile to your face when pushed down the stairs.




