a bit more info would help, what do you have running off the system, any modifications, vehicle, age ?

 

A multimeter would be a good investment. Start with the fuseboard.

Could be a dodgy switch? Is the second battery brand new?

 

Fit a fully charged battery and remove the earth wire then put a festune type bulb between the earth wire and the earth on the battery if the bulb glows you are drawing current then you can find out where the current is being drawn by removing your fuses one at a time and when the bulb stops working you know what area to look at

 

Thank I'll give a go
The second battery is brand new but it's naked that one too .no power what so ever from it ? It's a beetle 1957 12v alternator .