refactor: BatteryInfo structure (consistent layout)

- use tagged enum serialization for BatteryError
- flatten BatteryInfo telemetry with consistent field names and typed error

rust/src/hal/battery.rs

@@ -27,20 +27,22 @@ pub trait BatteryInteraction {
 
 #[derive(Debug, Serialize)]
 pub struct BatteryInfo {
-    pub voltage_milli_volt: u16,
-    pub average_current_milli_ampere: i16,
-    pub cycle_count: u16,
-    pub design_milli_ampere_hour: u16,
-    pub remaining_milli_ampere_hour: u16,
-    pub state_of_charge: f32,
-    pub state_of_health: u16,
-    pub temperature: u16,
+    pub voltage_mv: Option<u16>,
+    pub avg_current_ma: Option<i16>,
+    pub soc_pct: Option<f32>,
+    pub soh_pct: Option<u16>,
+    pub temperature_c: Option<u16>,
+    pub cycle_count: Option<u16>,
+    pub remaining_mah: Option<u16>,
+    pub design_mah: Option<u16>,
+    pub error: Option<BatteryError>,
 }
 
 #[derive(Debug, Serialize)]
+#[serde(tag = "kind")]
 pub enum BatteryError {
     NoBatteryMonitor,
-    CommunicationError(String),
+    CommunicationError { message: String },
 }
 
 #[derive(Debug, Serialize)]
@@ -180,14 +182,15 @@ impl BatteryInteraction for BQ34Z100G1 {
 
     async fn get_battery_state(&mut self) -> FatResult<BatteryState> {
         Ok(BatteryState::Info(BatteryInfo {
-            voltage_milli_volt: self.voltage_milli_volt().await?,
-            average_current_milli_ampere: self.average_current_milli_ampere().await?,
-            cycle_count: self.cycle_count().await?,
-            design_milli_ampere_hour: self.design_milli_ampere_hour().await?,
-            remaining_milli_ampere_hour: self.remaining_milli_ampere_hour().await?,
-            state_of_charge: self.state_charge_percent().await?,
-            state_of_health: self.state_health_percent().await?,
-            temperature: self.bat_temperature().await?,
+            voltage_mv: Some(self.voltage_milli_volt().await?),
+            avg_current_ma: Some(self.average_current_milli_ampere().await?),
+            soc_pct: Some(self.state_charge_percent().await?),
+            soh_pct: Some(self.state_health_percent().await?),
+            temperature_c: Some(self.bat_temperature().await?),
+            cycle_count: Some(self.cycle_count().await?),
+            remaining_mah: Some(self.remaining_milli_ampere_hour().await?),
+            design_mah: Some(self.design_milli_ampere_hour().await?),
+            error: None,
         }))
     }
 }