One of my friends wanted to learn to fly so on the cheap so I grabbed some free flight Art-tech Diamond 600 chuck gliders. I've converted similar types of models from other brands in the past so I know they can be cheap and near indestructible.
The battery sits in a cut out about the wing on CoG so it can be shifted forward or back as needed. It stays in place with a ton of Velcro lol. I used sharpie pens for some colour.