diff --git a/README.md b/README.md
index ade41ce..bfa70ea 100644
--- a/README.md
+++ b/README.md
@@ -1,7 +1,7 @@
 # DD3-LoRa-Bridge-MultiSender
 
 Unified firmware for LilyGO T3 v1.6.1 (ESP32 + SX1276 + SSD1306) running as either:
-- `Sender`: reads meter values and sends binary batches over LoRa.
+- `Sender`: reads energy-only values from multiple IEC 62056-21 meters and sends binary batches over LoRa.
 - `Receiver`: accepts batches, ACKs with optional time, publishes to MQTT/web.
 
 ## Protocol (minimal)
@@ -27,6 +27,9 @@ CRC16 validation is still required on every frame.
 ### 1) `BATCH_UP`
 - Uses existing binary batch/chunk transport.
 - `sample_count == 0` is valid and means `SYNC_REQUEST`.
+- Payload starts with `schema_id`:
+  - `0`: legacy schema (kept for compatibility)
+  - `1`: `EnergyMulti` schema (ts + integer kWh for up to 3 meters)
 
 ### 2) `ACK_DOWN` (7 bytes)
 - `flags` (`u8`): bit0 = `time_valid`
@@ -55,6 +58,37 @@ Only then:
 
 This guarantees no pre-`2026-02-01` epoch reaches MQTT or SD/DB paths.
 
+## Multi-meter sender mode
+
+- Meter protocol: IEC 62056-21 ASCII Mode D
+- UART framing: `9600 7E1`
+- Extracted OBIS: only total energy `1-0:1.8.0`
+- Conversion: kWh is sent as integer using `floor` (`12345.67 -> 12345`)
+
+### Meter count by build mode
+
+- Debug builds (`SERIAL_DEBUG_MODE=1`): `METER_COUNT=2`
+  - keeps USB serial logs on UART0
+  - uses UART1 + UART2 for meters
+- Prod builds (`SERIAL_DEBUG_MODE=0`): `METER_COUNT=3`
+  - no serial logging
+  - reclaims UART0 for meter 3 RX
+
+### Meter RX pins (TTGO T3 v1.6.1 defaults)
+
+- `PIN_METER1_RX = GPIO34` (UART2 RX)
+- `PIN_METER2_RX = GPIO25` (UART1 RX)
+- `PIN_METER3_RX = GPIO3` (UART0 RX, prod only)
+
+All pins are configurable in `include/config.h`.
+
+## Receiver MQTT output (EnergyMulti)
+
+For `schema_id=1`, MQTT payload includes integer fields:
+- `energy1_kwh`
+- `energy2_kwh`
+- `energy3_kwh` (when meter count is 3)
+
 ## Receiver behavior
 
 On `BATCH_UP`:
@@ -85,4 +119,5 @@ DS3231 RTC support was removed:
 ```bash
 pio run -e lilygo-t3-v1-6-1
 pio run -e lilygo-t3-v1-6-1-test
+pio run -e lilygo-t3-v1-6-1-prod
 ```