On 01/08/2018 10:06 PM, micky wrote:
Do these seem worth while? How can you get 300 or 500 amps out of a
little battery? How much does it really take to start a car when it has
a battery in it, that probably puts out a little? (apparently the
better model adn maybe t his one will charge the car's battery for 30
seconds if need be.)

For the same money you could just replace your car's weak battery with a new one from a bigboxstore.