Rack Battery with 3-Pin Plug

[Tubamanandy]

Anyone know the pin configuration for a rack battery with a 3-pin Kettle Plug ?

I basically want to check its voltage but just a bit unsure of where to stick the prongs.

 

[Deleted member 4366]

Only the outer two are used.

 

[Tubamanandy]

Thanks, I did wonder what the centre one was for