diff --git a/README.md b/README.md
index cda4709..e6f59ee 100644
--- a/README.md
+++ b/README.md
@@ -207,7 +207,7 @@ MeterBatch JSON (compressed over LoRa) uses per-field arrays with integer units
   "t_last": 1738288030,
   "dt_s": 1,
   "n": 3,
-  "energy_wh": [123456700, 123456701, 123456701],
+  "e_wh": [123456700, 123456701, 123456701],
   "p_w": [930, 940, 950],
   "p1_w": [480, 490, 500],
   "p2_w": [450, 450, 450],
diff --git a/src/json_codec.cpp b/src/json_codec.cpp
index 24a5017..e3e88c6 100644
--- a/src/json_codec.cpp
+++ b/src/json_codec.cpp
@@ -205,7 +205,7 @@ bool meterBatchToJson(const MeterData *samples, size_t count, uint16_t batch_id,
     doc["bat_v"] = serialized(bat_buf);
   }
 
-  JsonArray energy = doc.createNestedArray("energy_wh");
+  JsonArray energy = doc.createNestedArray("e_wh");
   JsonArray p_w = doc.createNestedArray("p_w");
   JsonArray p1_w = doc.createNestedArray("p1_w");
   JsonArray p2_w = doc.createNestedArray("p2_w");
@@ -258,7 +258,7 @@ bool jsonToMeterBatch(const String &json, MeterData *out_samples, size_t max_cou
     uint32_t t_first = doc["t_first"] | t0;
     uint32_t t_last = doc["t_last"] | t_first;
     uint32_t dt_s = doc["dt_s"] | 1;
-    JsonArray energy = doc["energy_wh"].as<JsonArray>();
+    JsonArray energy = doc["e_wh"].as<JsonArray>();
     JsonArray p_w = doc["p_w"].as<JsonArray>();
     JsonArray p1_w = doc["p1_w"].as<JsonArray>();
     JsonArray p2_w = doc["p2_w"].as<JsonArray>();
diff --git a/src/main.cpp b/src/main.cpp
index eb12144..c795fe3 100644
--- a/src/main.cpp
+++ b/src/main.cpp
@@ -81,6 +81,7 @@ static uint16_t g_last_sent_batch_id = 0;
 static uint16_t g_last_acked_batch_id = 0;
 static uint8_t g_batch_retry_count = 0;
 static bool g_batch_ack_pending = false;
+static uint32_t g_batch_ack_timeout_ms = BATCH_ACK_TIMEOUT_MS;
 static MeterData g_inflight_samples[METER_BATCH_MAX_SAMPLES];
 static uint8_t g_inflight_count = 0;
 static uint16_t g_inflight_batch_id = 0;
@@ -294,6 +295,17 @@ static uint32_t compute_batch_rx_timeout_ms(uint16_t total_len, uint8_t chunk_co
   return timeout_ms < 10000 ? 10000 : timeout_ms;
 }
 
+static uint32_t compute_batch_ack_timeout_ms(size_t payload_len) {
+  if (payload_len == 0) {
+    return 10000;
+  }
+  uint8_t chunk_count = static_cast<uint8_t>((payload_len + BATCH_CHUNK_PAYLOAD - 1) / BATCH_CHUNK_PAYLOAD);
+  size_t packet_len = 5 + BATCH_HEADER_SIZE + (payload_len > BATCH_CHUNK_PAYLOAD ? BATCH_CHUNK_PAYLOAD : payload_len) + 2;
+  uint32_t per_chunk_toa_ms = lora_airtime_ms(packet_len);
+  uint32_t timeout_ms = static_cast<uint32_t>(chunk_count) * per_chunk_toa_ms + BATCH_RX_MARGIN_MS;
+  return timeout_ms < 10000 ? 10000 : timeout_ms;
+}
+
 static bool inject_batch_meta(String &json, int16_t rssi_dbm, float snr_db, uint32_t rx_ts_utc) {
   DynamicJsonDocument doc(8192);
   DeserializationError err = deserializeJson(doc, json);
@@ -423,6 +435,7 @@ static bool send_inflight_batch(uint32_t ts_for_display) {
   if (SERIAL_DEBUG_MODE && compress_ms > 200) {
     serial_debug_printf("tx: compress took %lums", static_cast<unsigned long>(compress_ms));
   }
+  g_batch_ack_timeout_ms = compute_batch_ack_timeout_ms(compressed_len);
 
   uint32_t send_start = millis();
   bool ok = send_batch_payload(compressed, compressed_len, ts_for_display, g_inflight_batch_id);
@@ -668,6 +681,29 @@ static void sender_loop() {
     send_meter_batch(last_sample_ts());
   }
 
+  if (g_batch_ack_pending) {
+    uint32_t end_ms = millis() + 400;
+    while (millis() < end_ms) {
+      LoraPacket ack_pkt = {};
+      if (!lora_receive(ack_pkt, 0) || ack_pkt.protocol_version != PROTOCOL_VERSION) {
+        delay(5);
+        continue;
+      }
+      if (ack_pkt.payload_type == PayloadType::Ack && ack_pkt.payload_len >= 6 && ack_pkt.role == DeviceRole::Receiver) {
+        uint16_t ack_id = read_u16_le(ack_pkt.payload);
+        uint16_t ack_sender = read_u16_le(&ack_pkt.payload[2]);
+        uint16_t ack_receiver = read_u16_le(&ack_pkt.payload[4]);
+        if (ack_sender == g_short_id && ack_receiver == ack_pkt.device_id_short &&
+            g_batch_ack_pending && ack_id == g_last_sent_batch_id) {
+          g_last_acked_batch_id = ack_id;
+          serial_debug_printf("ack: ok batch_id=%u", ack_id);
+          finish_inflight_batch();
+          break;
+        }
+      }
+    }
+  }
+
   LoraPacket rx = {};
   if (lora_receive(rx, 0) && rx.protocol_version == PROTOCOL_VERSION) {
     if (rx.payload_type == PayloadType::TimeSync) {
@@ -685,7 +721,7 @@ static void sender_loop() {
     }
   }
 
-  if (g_batch_ack_pending && (now_ms - g_last_batch_send_ms >= BATCH_ACK_TIMEOUT_MS)) {
+  if (g_batch_ack_pending && (now_ms - g_last_batch_send_ms >= g_batch_ack_timeout_ms)) {
     if (g_batch_retry_count < BATCH_MAX_RETRIES) {
       g_batch_retry_count++;
       serial_debug_printf("ack: timeout batch_id=%u retry=%u", g_inflight_batch_id, g_batch_retry_count);