Power Supply Unit on or off?

[kc22]

Dumb question time as first time campervan owner.

I have a T32 T6.1 Transporter conversion and the main battery drops quickly. In an attempt to find a solution I'm looking at what needs to be switched off when not in use.

I have the (attached) power supply unit in the van but my question is should I turn it off when I'm not using the van?

I've only had the van a few weeks and it's been left one since I bought it home.

 

[CAB]

I would turn it off when not using it. Shouldn't draw too much but it all counts.