My preferred choice (yes, it's a bit anal) is to charge my 12v slave battery. Let it stand for about 12 hours to stabilise. Connect the charge lead to the box making sure the two croc clips do not touch. Then connect to the slave battery. Leave to charge for about 8 hours if the box is dead flat. When disconnecting make sure you don't short the battery leads !
It is worth checking part way through to see how warm the Interspan box is getting. They are usually just warm to the touch unless you have just had new rechargeable batteries fitted. In which case they get much much warmer for the first few charges.
I now run the new type cells in my old 1988 box. They last so much longer. I can get at least 4-5 races from a single charge.
Make sure you run non-resistor spark plugs and caps.
