I use a 4-pin circular connector from Cole-Hersee. It's mounted inside the oil dip stick door, attached to the engine mount with an MS21919-DG clamp. I've wired two pins to battery (-) and two pins to battery (+) via an in-line fuse, using 18ga wire. The contacts in this connector are brass and quite heavy-duty so I have had no trouble passing full battery charging current through it and running our entire aircraft.
Buy a spare matching 4-pin plug and wire it up with decent-sized alligator clips. Keep it in your fly-away kit so you can easily recharge your battery while away from home.