Actually a cars battery and electrical system is about 13V to 14V. So 6 amps is about 80 Watts. Also factoring in alternator efficiency should be done.
80/745.7 = 0.11 (0.10728)
0.10728/ .7 = 0.153 HP
In reality it would be more HP than this because I used a very high value for alternator efficiency.
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