In order to save weight, the Atom uses a small, lightweight Braille B20145 battery. If you let the Atom sit for over a month, the battery will likely run down (the immobilizer circuit is always active). The Braille battery is a combination of expensive and hard-to-get (around $150, over a month lead time) so you don't want to ruin one if you can help it. I purchased a Battery Tender Plus model and mounted it on a shelf in the garage:

Battery tender and Atom

I used the ring terminal cable to attach it to the Atom. This cable has rings that screw onto the Atom's battery terminals. I routed the free end of the cable out the upper left A-arm. You can also see the rubber dust cap that covers the car end of the connector when the battery tender is disconnected:

Close-up of connectors

The streamer is an aircraft "Remove before starting engine" warning streamer, which reminds me to disconnect the battery tender before moving the Atom:

Warning streamer