Oh yes I remember them. They used to fail occasionally.
In my old Bedford CA van I had a second battery and a big round red switch that was off a yacht. The switch brought the second battery into use when required. I could have battery A, battery B, or both at once. This was so I could work at night with various lights on and yet still be sure of the van starting. On a really cold morning I'd have both batteries connected to start the van. It made a lot of difference.
I also remember a neighbour who started his 12VDC petrol engined lorry by means of a second battery, but he connected it in series! It never seemed to do any harm, and it certainly turned the engine over.
Also, who remembers
-- the business of building a fire under the diesel tank when it was really cold?
-- winding the window down and using a Fairy liquid bottle full of water to clean the windscreen, because screenwashers weren't fitted?
-- then, later, fitting a screenwasher kit so the MOT could be passed?
Leaving a paraffin lamp under the engine at night in the hope that it would help the car to start? (it worked, but there was a risk...)
Hanging a paraffin road lamp on the driver's door handle when parked to comply with the law? (as kids we used to steal them)
Manually changing the tyres round to even up the wear?
Running a mains lead across the pavement so the battery could be on charge all night? (the short run to and from work with the lights on wouldn't recharge the battery: the dynamo was rated at 22A and then only when you were doing 60mph!)
Bill