As the D90s are not used every day, it’s wise that we look after the on-board batteries. I recommend the CTEK maintenance chargers, which are easy to mount on-board (I have the US800 model installed under the seat in the Defenders). 

However, connecting an extension cord currently involves crawling under the truck, removing a waterproof cap and plugging in the extension - not ideal, you get grubby and it is a little vulnerable to rock damage. 

I discovered that Marinco/Guest make some great electrical accessories designed for marine use as part of the “ConnectCharge” system. It does what it says on the can, it connects your internal charger to the shore supply. I picked up a couple of ConnectCharge Inlets (P/N 150CCI) and some ConnectCharge cords (P/N 157200) which clip together to make a robust system (BTW, I ordered them from http://www.stayonline.com). 

Now the inlet requires a 1-7/8” hole. I’ll be mounting mine on the wing vents, which means I can easily replace the vent cover and I won’t damage the wing. Coupled with two retractable power extension cords, which will plug into the ConnectCharge inlets I think I’ll have a much better system. 

Of course, the ultimate solution is to have an automatic ejection system, like the Kussmaul Super Auto Eject, as found in emergency vehicles.