Add battery changed callbacks (#25207)

docs/drivers/battery.md

@@ -49,3 +49,25 @@ Sample battery level.
 #### Return Value {#api-battery-get-percent-return}
 
 The battery percentage, in the range 0-100.
+
+## Callbacks
+
+### `void battery_percent_changed_user(uint8_t level)` {#api-battery-percent-changed-user}
+
+User hook called when battery level changed.
+
+### Arguments {#api-battery-percent-changed-user-arguments}
+
+ - `uint8_t level`  
+   The battery percentage, in the range 0-100.
+
+---
+
+### `void battery_percent_changed_kb(uint8_t level)` {#api-battery-percent-changed-kb}
+
+Keyboard hook called when battery level changed.
+
+### Arguments {#api-battery-percent-changed-kb-arguments}
+
+ - `uint8_t level`  
+   The battery percentage, in the range 0-100.

drivers/battery/battery.c

@@ -17,11 +17,21 @@ void battery_init(void) {
     last_bat_level = battery_driver_sample_percent();
 }
 
+__attribute__((weak)) void battery_percent_changed_user(uint8_t level) {}
+__attribute__((weak)) void battery_percent_changed_kb(uint8_t level) {}
+
+static void handle_percent_changed(void) {
+    battery_percent_changed_user(last_bat_level);
+    battery_percent_changed_kb(last_bat_level);
+}
+
 void battery_task(void) {
     static uint32_t bat_timer = 0;
     if (timer_elapsed32(bat_timer) > BATTERY_SAMPLE_INTERVAL) {
         last_bat_level = battery_driver_sample_percent();
 
+        handle_percent_changed();
+
         bat_timer = timer_read32();
     }
 }

drivers/battery/battery.h

@@ -31,4 +31,16 @@ void battery_task(void);
  */
 uint8_t battery_get_percent(void);
 
+/**
+ * \brief user hook called when battery level changed.
+ *
+ */
+void battery_percent_changed_user(uint8_t level);
+
+/**
+ * \brief keyboard hook called when battery level changed.
+ *
+ */
+void battery_percent_changed_kb(uint8_t level);
+
 /** \} */