Both the LX Navigation Colibri II or the LXNav Nano 3 are nice small backups as they are IGC approved loggers, audio varios, thermal optimizers, and GPS navigation tools with internal batteries. Outside the scope of this discussion of "I lost all my power!" is that they can also can display FLARM with an external input (FLARM brick or portable).

Colibri II is less expensive (still being sold?).
Nano 3 seems brighter (better ease of use?).

Videos
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Colibri II https://www.youtube.com/watch?v=G_pl9iLpxAc
Nano 3 https://www.youtube.com/watch?v=SG6zwEtCs9k