As Dirk said, primarily for the purpose of getting the most out of a glider design. It could probably handle more weight, but would defeat the purpose of optimizing a glider.
The Lancer has a long nose, but a long tail also. I'd probably want the battery hatch to allow for a wide variation of adjustment, unless of course the hatch opening is framed in at the point of near completion, where the CG can be positively determined. Something like this idea, other than personally preferring bottom hatches for appearance:
https://www.google.com/search?q=guillow ... VdT-kFM%3AOTOH if I was using a brick for RET, I'd probably want the brick located in the forward cabin area, leaving the entire nose length for battery adjustment. Depending on how it's built (covering weight, motor weight, painted or not, etc...) the battery location required to set the CG could vary widely.