I use a couple of these. See
https://www.jaycar.com.au/12vdc-3a-c...utlet/p/MP3671
I have an old Meade 2080 GEM that is reverse polarity to everything else I have so I got it it’s own controller. The polarity is easily changed by reversing the plug pins. The voltage is selectable via the red dial. If you have a battery just get a separate cig lighter socket with leads like
https://www.jaycar.com.au/cigarette-...clips/p/PP2007
(I’d cut the clips off and put on insulated spade lugs to avoid shorting the battery in the dark). Amazon Au has heaps on offer too as far as automotive battery accessories go.
The Harley Benton unit looks good though and price is reasonable but yes output needs to hit a bit more for most astronomy use. Also 5.1V USB output would be handy to have on board too (a few sockets at different Watts).