fuel_gauge: Add basic stub API doc.

Add a short stub doc as a placeholder for future documentation on the fuel
gauge API.

Signed-off-by: Aaron Massey <aaronmassey@google.com>

doc/develop/api/overview.rst

@@ -109,6 +109,10 @@ between major releases are available in the :ref:`zephyr_release_notes`.
      - Stable
      - 1.11
 
+   * - :ref:`fuel_gauge_api`
+     - Experimental
+     - 3.3
+
    * - :ref:`flash_map_api`
      - Stable
      - 1.11

doc/hardware/peripherals/fuel_gauge.rst

@@ -0,0 +1,37 @@
+.. _fuel_gauge_api:
+
+Fuel Gauges (Experimental API Stub Doc)
+#######################################
+
+The fuel gauge subsystem exposes an API to uniformly access battery fuel gauge devices. Currently,
+only reading data is supported.
+
+Note: This API is currently experimental and this doc will be significantly changed as new features
+are added to the API.
+
+Basic Operation
+***************
+
+Properties
+==========
+
+Fundamentally, a property is a quantity that a fuel gauge device can measure.
+
+Fuel gauges typically support multiple properties, such as temperature readings of the battery-pack
+or present-time current/voltage.
+
+Properties are fetched using a client allocated array of :c:struct:`fuel_gauge_get_property`.  This
+array is then populated by values as according to its `property_type` field.
+
+Caching
+=======
+
+The Fuel Gauge API explicitly provides no caching for its clients.
+
+
+.. _fuel_gauge_api_reference:
+
+API Reference
+*************
+
+.. doxygengroup:: fuel_gauge_interface

doc/hardware/peripherals/index.rst

@@ -20,6 +20,7 @@ Peripherals
    eeprom.rst
    entropy.rst
    flash.rst
+   fuel_gauge.rst
    gna.rst
    gpio.rst
    hwinfo.rst

include/zephyr/drivers/fuel_gauge.h

@@ -7,6 +7,13 @@
 #ifndef ZEPHYR_INCLUDE_DRIVERS_BATTERY_H_
 #define ZEPHYR_INCLUDE_DRIVERS_BATTERY_H_
 
+/**
+ * @brief Fuel Gauge Interface
+ * @defgroup fuel_gauge_interface Fuel Gauge Interface
+ * @ingroup io_interfaces
+ * @{
+ */
+
 #ifdef __cplusplus
 extern "C" {
 #endif /* __cplusplus */
@@ -128,6 +135,10 @@ __subsystem struct battery_driver_api {
 	fuel_gauge_get_property_t get_property;
 };
 
+/**
+ * @}
+ */
+
 #ifdef __cplusplus
 }
 #endif /* __cplusplus */