feat(ble): Only update BAS when active

Subscribes to the activity changing event, will stop the battery work timer when in idle or deep sleep, restart when board goes active

app/src/battery.c

@@ -18,6 +18,8 @@ LOG_MODULE_DECLARE(zmk, CONFIG_ZMK_LOG_LEVEL);
 #include <zmk/event_manager.h>
 #include <zmk/battery.h>
 #include <zmk/events/battery_state_changed.h>
+#include <zmk/events/activity_state_changed.h>
+#include <zmk/activity.h>
 #include <zmk/workqueue.h>
 
 static uint8_t last_state_of_charge = 0;
@@ -105,4 +107,26 @@ static int zmk_battery_init(const struct device *_arg) {
     return 0;
 }
 
+static int battery_event_listener(const zmk_event_t *eh) {
+
+    if (as_zmk_activity_state_changed(eh)) {
+        switch (zmk_activity_get_state()) {
+        case ZMK_ACTIVITY_ACTIVE:
+            k_timer_start(&battery_timer, K_NO_WAIT, K_SECONDS(CONFIG_ZMK_BATTERY_REPORT_INTERVAL));
+            return 0;
+        case ZMK_ACTIVITY_IDLE:
+        case ZMK_ACTIVITY_SLEEP:
+            k_timer_stop(&battery_timer);
+            return 0;
+        default:
+            break;
+        }
+    }
+    return -ENOTSUP;
+}
+
+ZMK_LISTENER(battery, battery_event_listener);
+
+ZMK_SUBSCRIPTION(battery, zmk_activity_state_changed);
+
 SYS_INIT(zmk_battery_init, APPLICATION, CONFIG_APPLICATION_INIT_PRIORITY);