off topic
Before auto electrical became so sensitive I had an eight volt and a six volt battery series in the back of my service pickup for winter jump starting.
Both batteries were within 5% of amp hours of each other.
And each got recharged separately.
I connected jumper cables to the vehicle to be started
Then asked the driver to twist the key and hold it
I would then press an underhood button to trigger a starter relay
Rrrr...Rrrr...Rrrr...(click)...WAHHHHHHHHHHHH!
Not recommended with today's ECU's
But it brings forth warm memories. I would be called to start cars in the 70's when tow truck drivers wanted to tow.