TDA7492 Power

[modernjack3]

So ist me , the car battery guy again and I am having a big Problem - I just figured out tht my battery guard isnt really made for Music use since this Is a Wave and no constant current - and I just wondered if I could do it by time instead - Can I use the datasheet of the TDA7492 and the 8 Ohm load curve ?I want to get my supply voltage for this board : https://www.amazon.com/KKmoon-Wireless-Bluetooth-2-channel-Amplifier/dp/B01BV8LM5Q down to 13 V so it can Output a MAX of ~15 W per channel ( says the datasheet) is my thought correct ? Does the datasheet even fit to my board or is there a step up conv built in ?  so many questions ...

Datasheet : http://www.st.com/content/ccc/resource/technical/document/datasheet/f4/3e/da/a3/97/e7/4f/8d/CD00205863.pdf/files/CD00205863.pdf/jcr:content/translations/en.CD00205863.pdf

8 Ohm caracteristics..

Greetings Jack !

PS : My battery says "650W if discharged over 20 Hrs" so id like it to drain about 32W