Panels are similar to Battens in terms of application (designed to replace 2ft, 4ft and 5ft fluorescent T8/T5 tubes in both single and twin formation).
The key difference between Panels and Battens is aesthetics. Panels are thin rectangle or square type fittings that are either surface mounted or recessed into a ceiling troffer; so, the ceiling appears smooth and flat. E.g. the lights do not protrude, but rather merge into the ceiling surface to minimise visual impact.