diff --git a/mobile/db/sync.ts b/mobile/db/sync.ts
index f17f7d6..5e010b0 100644
--- a/mobile/db/sync.ts
+++ b/mobile/db/sync.ts
@@ -1,3 +1,4 @@
+import * as FileSystem from 'expo-file-system/legacy';
 import type { SQLiteDatabase } from 'expo-sqlite';
 import { getSetting, upsertRemoteActivity } from './queries';
 
@@ -158,8 +159,14 @@ async function uploadLocalActivities(
   token: string,
   onProgress?: (n: number, total: number) => void,
 ): Promise<{ uploaded: number; failed: number }> {
-  const rows = db.getAllSync<{ id: string; detail_json: string; timeseries_json: string | null; geojson: string | null }>(
-    `SELECT id, detail_json, timeseries_json, geojson
+  const rows = db.getAllSync<{
+    id: string;
+    detail_json: string;
+    timeseries_json: string | null;
+    geojson: string | null;
+    original_path: string | null;
+  }>(
+    `SELECT id, detail_json, timeseries_json, geojson, original_path
      FROM activities WHERE origin = 'local' AND synced_at IS NULL`,
   );
 
@@ -173,28 +180,44 @@ async function uploadLocalActivities(
     const row = rows[i];
     onProgress?.(i + 1, total);
     try {
-      const detail = JSON.parse(row.detail_json);
-      const activity = { id: row.id, ...detail };
+      let resp: Response;
 
-      const body: Record<string, unknown> = { activity };
-      if (row.timeseries_json) body.timeseries = JSON.parse(row.timeseries_json);
-      if (row.geojson)         body.geojson    = JSON.parse(row.geojson);
+      // Prefer raw upload when the original FIT/GPX/TCX file is still on disk.
+      // The server re-extracts it with DEM elevation correction, producing better data.
+      const useRaw = row.original_path !== null &&
+        (await FileSystem.getInfoAsync(row.original_path)).exists;
 
-      const resp = await fetch(`${instanceUrl}/api/upload/bas`, {
-        method: 'POST',
-        headers,
-        body: JSON.stringify(body),
-      });
+      if (useRaw) {
+        const filename = row.original_path!.split('/').pop() ?? 'activity.fit';
+        const base64 = await FileSystem.readAsStringAsync(row.original_path!, {
+          encoding: FileSystem.EncodingType.Base64,
+        });
+        resp = await fetch(`${instanceUrl}/api/upload/raw`, {
+          method: 'POST',
+          headers,
+          body: JSON.stringify({ filename, base64 }),
+        });
+      } else {
+        const detail = JSON.parse(row.detail_json);
+        const body: Record<string, unknown> = { activity: { id: row.id, ...detail } };
+        if (row.timeseries_json) body.timeseries = JSON.parse(row.timeseries_json);
+        if (row.geojson)         body.geojson    = JSON.parse(row.geojson);
+        resp = await fetch(`${instanceUrl}/api/upload/bas`, {
+          method: 'POST',
+          headers,
+          body: JSON.stringify(body),
+        });
+      }
 
       if (resp.ok) {
         await db.runAsync(`UPDATE activities SET synced_at = ? WHERE id = ?`, [now, row.id]);
         uploaded++;
       } else {
-        console.warn(`upload/bas ${row.id}: HTTP ${resp.status}`);
+        console.warn(`upload ${row.id}: HTTP ${resp.status}`);
         failed++;
       }
     } catch (err) {
-      console.warn(`upload/bas ${row.id}:`, err);
+      console.warn(`upload ${row.id}:`, err);
       failed++;
     }
   }