Once the push pins are removed from the battery cover (by pushing the center of the pins in until they click) the battery cover can be prised off (there are two clips at the other end) just pull it off.
The positive battery terminal connections are under a red plastic cover held with two clips, a bit fiddly, but it does come off. Be careful as this exposes a live terminal. There is some spare thread on a bolt, so if you can find a nut to fit, it's the ideal fixing point. For the negative there is a bolt in the floor.
I have put a Bluetooth monitor here & the connector that comes with my Ctec charger.
You will see there is a small box with cover in the battery cover, there is no back to this & the Ctec plug fits in there nicely, then replace the battery cover, locating the fixed clips first, then push the center pins in the push pins out, until they click & put push pins into the cover, lastly pushing the center pins back in.
The Ctec plug can be accessed by removing the small, square cover in the battery cover for easy charging of the 12v battery.
I hope this is not too long winded & helps someone, just be careful not to short out the positive terminal.