Update README.md

extras/cad/README.md

@@ -11,6 +11,6 @@
 - `aprs_tracker_e22_cover` - upper cover for headless tracker without any controls.
 - `aprs_tracker_e22_antenna_ring` - TPU filament ring placed under antenna.
 - `aprs_tracker_e22_base_battery_lid` - lid for battery compartment.
-- `aprs_tracker_e22_base_battery` - base for tracker case with battery compartment.
+- `aprs_tracker_e22_base_battery` - base for tracker case with battery compartment (for single 18650 with charging + dc-dc 5v converter).
 - `aprs_tracker_e22_cover_dv` - DV cover version with holes for screen, encoder, ptt button, speaker, mic.
 - `aprs_tracker_e22_encoder_knob` - knob for encoder.