Assuming a typical lead-acid, 12 V car battery (typically at 13 V or so fully charged), and that it takes roughly 500 A over 3 seconds to start an engine, how long will it take to recharge the battery at any given charge rate?
Here's my attempt from what I remember about physics:
12.8 V * 500 A = 6400 W
Over 3 seconds that's 19,200 joules.
So, in a perfect world where all the current goes right back in to the battery and whatnot, how long does it take to regain all my joules and put them back in my battery?
Given a 2A charge rate:
14 V (output of charger?) * 2 A = 28 watts
Here's where I'm a little shaky. What's next? Divide the joules by the wattage to get time? Seems like it:
19,200 joules / 28 watts = 11.4 minutes.
That's it? 11.4 minutes at 2 A and all 19,200 joules are back? Seems hard to believe. My charger also has a 10A setting. So that means in about 2.5 minutes, it'll be "recharged".
So, are my assumptions correct? Do you really just use the charging voltage to calculate this, it seems like you would need to put the charging voltage in relation to the battery's capacity/voltage/whatever.