Implement Battery Telemetry

**Description:**
Use BatteryManager and Intent.ACTION_BATTERY_CHANGED to get battery percentage, charging status, and health. Store in BatteryInfo.

**Acceptance Criteria:**

- [ ]  Implement battery retrieval function
- [ ]  Return BatteryInfo object
- [ ]  Test on device
- [ ]  Commit and push

**Estimated Effort:** 1-2 hours