battery: centralized LiPo OCV curve + ADC multiplier corrections

Add a board-aware battery SOC system replacing the two independent
linear approximations that existed in the UI helpers.

New helpers/battery_curve.{h,c}: a 21-point (5% step) OCV lookup table
with integer linear interpolation. The default generic LiPo curve is a
weak symbol — any board can override it by dropping a battery_curve.c
into its board directory. CMakeLists.txt selects the board-specific file
when present, falling back to the generic.

Board.h gains getBattPercent() (default 0); ZephyrBoard implements it
via battery_curve_lookup().

Board-specific curves added for boards with measured cell data:
t1000_e, rak_wismesh_tag, thinknode_m6, sensecap_solar, wio_tracker_l1.

ADC multiplier corrections applied across all nRF52840 boards:
- Boards using a correctly-derived 3600×ratio formula get +0.5% to
  compensate for nRF SAADC gain error (7200→7236, 6300→6332, etc.)
- rak_wismesh_tag, rak3401_1watt, gat562_30s had multipliers copied
  from Arduino's 3.0V AREF formula; corrected to 3600×1.73×1.005=6259
- xiao_nrf52840 (10911) left unchanged — empirically calibrated value
  above the theoretical, assumed already correct for that hardware

get adc.multiplier now reports current mV reading and the board's
curve 100% target, making field calibration self-guiding.

zephcore/CMakeLists.txt

@@ -436,6 +436,21 @@ target_sources(app PRIVATE
   helpers/fatal_reboot.c
 )
 
+# ========== Battery Curve Selection ==========
+# Board-specific battery_curve.c wins over the generic default.
+# To add a curve for a board, create boards/<platform>/<board>/battery_curve.c
+# without __weak — the linker prefers the non-weak generic only as a fallback.
+file(GLOB_RECURSE _BOARD_BATTERY_CURVE
+     "${CMAKE_CURRENT_SOURCE_DIR}/boards/*/${BOARD_BASE}/battery_curve.c")
+if(_BOARD_BATTERY_CURVE)
+  list(GET _BOARD_BATTERY_CURVE 0 _BOARD_BATTERY_CURVE)
+  message(STATUS "ZephCore Battery: board-specific curve (${_BOARD_BATTERY_CURVE})")
+  target_sources(app PRIVATE "${_BOARD_BATTERY_CURVE}")
+else()
+  message(STATUS "ZephCore Battery: generic LiPo curve")
+  target_sources(app PRIVATE helpers/battery_curve.c)
+endif()
+
 # Native-Linux (native_sim) runtime setup: force real-time clock mode so the
 # simulated clock tracks wall time (required for the real SX126x radio's
 # BUSY/DIO1 timing).  Bakes in the equivalent of the --rt command-line flag.

zephcore/adapters/board/ZephyrBoard.cpp

@@ -3,6 +3,7 @@
  */
 
 #include "ZephyrBoard.h"
+#include "battery_curve.h"
 #include <zephyr/kernel.h>
 #include <zephyr/sys/reboot.h>
 #include <zephyr/drivers/sensor.h>
@@ -146,6 +147,11 @@ uint16_t ZephyrBoard::getBattMilliVolts()
 #endif
 }
 
+uint8_t ZephyrBoard::getBattPercent()
+{
+	return battery_curve_lookup(&battery_curve_default, getBattMilliVolts());
+}
+
 bool ZephyrBoard::setAdcMultiplier(float multiplier)
 {
 #if DT_NODE_EXISTS(DT_PATH(zephyr_user)) && \

zephcore/adapters/board/ZephyrBoard.h

@@ -12,6 +12,7 @@ namespace mesh {
 class ZephyrBoard : public MainBoard {
 public:
 	uint16_t getBattMilliVolts() override;
+	uint8_t  getBattPercent() override;
 	float getMCUTemperature() override;
 	bool setAdcMultiplier(float multiplier) override;
 	float getAdcMultiplier() const override;

zephcore/boards/nrf52840/gat562_30s/gat562_30s.dts

@@ -146,7 +146,7 @@
 	/* Battery sense: AIN3 = P0.05 with the GAT562 divider (~1.73x) */
 	zephyr,user {
 		io-channels = <&adc 3>;
-		vbat-mv-multiplier = <6232>;	/* mv = raw * multiplier / 4096 */
+		vbat-mv-multiplier = <6259>;	/* 1.73:1 divider, 3.6V ref; corrected from Arduino 3.0V AREF + nRF SAADC gain */
 	};
 };
 

zephcore/boards/nrf52840/heltec_t114/heltec_t114_nrf52840.dts

@@ -182,7 +182,7 @@
 		 * voltage divider ratio = 4.9 (ADC_MULTIPLIER from variant.h).
 		 * multiplier = 3600 * 4.9 = 17640
 		 */
-		vbat-mv-multiplier = <17640>;
+		vbat-mv-multiplier = <17728>;  /* 4.9:1 divider, 3.6V ref; +0.5% for nRF SAADC gain error */
 	};
 
 	aliases {

zephcore/boards/nrf52840/ikoka_nano_30dbm/ikoka_nano_30dbm.dts

@@ -72,7 +72,7 @@
 	/* Battery ADC channel */
 	zephyr,user {
 		io-channels = <&adc 7>;
-		vbat-mv-multiplier = <10650>;  /* 1M/510k divider (2.96x), 3.6V ref */
+		vbat-mv-multiplier = <10709>;  /* 2.96:1 divider, 3.6V ref; +0.5% for nRF SAADC gain error */
 	};
 };
 

zephcore/boards/nrf52840/lilygo_techo/lilygo_techo.dts

@@ -190,7 +190,7 @@
 	 * with ADC_REF_INTERNAL (0.6V) × gain 1/6 × divider 2.0. */
 	zephyr,user {
 		io-channels = <&adc 2>;
-		vbat-mv-multiplier = <7200>;
+		vbat-mv-multiplier = <7236>;  /* 2:1 divider, 3.6V ref; +0.5% for nRF SAADC gain error */
 	};
 
 	/* ---- E-Paper display (MIPI DBI SPI) ----

zephcore/boards/nrf52840/promicro_lr2021/promicro_lr2021.dts

@@ -77,7 +77,7 @@
 	/* Battery ADC: P0.31 (AIN7), 150K+150K voltage divider (2:1) */
 	zephyr,user {
 		io-channels = <&adc 7>;
-		vbat-mv-multiplier = <7200>;
+		vbat-mv-multiplier = <7236>;  /* 2:1 divider, 3.6V ref; +0.5% for nRF SAADC gain error */
 	};
 };
 

zephcore/boards/nrf52840/promicro_sx1262/promicro_sx1262.dts

@@ -78,7 +78,7 @@
 	/* Battery ADC: P0.31 (AIN7), 2:1 voltage devider, 3.6V ref */
 	zephyr,user {
 		io-channels = <&adc 7>;
-		vbat-mv-multiplier = <7200>;
+		vbat-mv-multiplier = <7236>;  /* 2:1 divider, 3.6V ref; +0.5% for nRF SAADC gain error */
 	};
 };
 

zephcore/boards/nrf52840/rak3401_1watt/rak3401_1watt.dts

@@ -94,7 +94,7 @@
 	 * vbat-mv-multiplier = round(3 * 1.73 * 1.187 * 1000) = 6161 */
 	zephyr,user {
 		io-channels = <&adc 3>;
-		vbat-mv-multiplier = <6161>;
+		vbat-mv-multiplier = <6259>;  /* 1.73:1 divider, 3.6V ref; corrected from Arduino 3.0V AREF + nRF SAADC gain */
 	};
 };
 

zephcore/boards/nrf52840/rak_wismesh_tag/battery_curve.c

@@ -0,0 +1,26 @@
+/*
+ * SPDX-License-Identifier: Apache-2.0
+ *
+ * RAK WisMesh Tag single-cell LiPo OCV curve — 21 points at 5% steps.
+ * 11-point base linearly interpolated to 5% resolution.
+ * Index 0 = 100% (4160 mV), index 20 = 0% (2990 mV).
+ *
+ * Notable shape: very compressed upper range (100% = 4160 mV, not 4190),
+ * flat plateau 3.72–3.76 V, steep cliff below 3.62 V to 2990 mV cutoff.
+ */
+
+#include "battery_curve.h"
+
+static const uint16_t ocv_rak_wismesh_tag[21] = {
+	4160, 4090, 4020, 3980, 3940, /* 100 .. 80% */
+	3905, 3870, 3840, 3810, 3785, /*  75 .. 55% */
+	3760, 3750, 3740, 3730, 3720, /*  50 .. 30% */
+	3700, 3680, 3650, 3620, 3305, /*  25 ..  5% */
+	2990,                          /*   0%       */
+};
+
+const battery_curve_t battery_curve_default = {
+	.ocv_mv     = ocv_rak_wismesh_tag,
+	.num_points = 21,
+	.num_cells  = 1,
+};

zephcore/boards/nrf52840/rak_wismesh_tag/rak_wismesh_tag.dts

@@ -138,7 +138,7 @@
 	 * applied to 12-bit average with default ref (GAIN_1_6 + 0.6V internal = 3.6V FS). */
 	zephyr,user {
 		io-channels = <&adc 3>;
-		vbat-mv-multiplier = <6161>;
+		vbat-mv-multiplier = <6259>;  /* 1.73:1 divider, 3.6V ref; corrected from Arduino 3.0V AREF + nRF SAADC gain */
 	};
 
 	/* ---- Buzzer on PWM0 ---- */

zephcore/boards/nrf52840/sensecap_solar/battery_curve.c

@@ -0,0 +1,27 @@
+/*
+ * SPDX-License-Identifier: Apache-2.0
+ *
+ * SenseCAP Solar single-cell LiPo OCV curve — 21 points at 5% steps.
+ * 11-point base linearly interpolated to 5% resolution.
+ * Index 0 = 100% (4200 mV), index 20 = 0% (2786 mV).
+ *
+ * Notable shape: steeper overall slope than a standard LiPo, consistent with
+ * a high-impedance cell measured under load rather than at true OCV. Low
+ * cutoff (2786 mV) reflects the solar node's extended discharge budget.
+ */
+
+#include "battery_curve.h"
+
+static const uint16_t ocv_sensecap_solar[21] = {
+	4200, 4093, 3986, 3954, 3922, /* 100 .. 80% */
+	3867, 3812, 3773, 3734, 3689, /*  75 .. 55% */
+	3645, 3586, 3527, 3473, 3420, /*  50 .. 30% */
+	3350, 3281, 3184, 3087, 2936, /*  25 ..  5% */
+	2786,                          /*   0%       */
+};
+
+const battery_curve_t battery_curve_default = {
+	.ocv_mv     = ocv_sensecap_solar,
+	.num_points = 21,
+	.num_cells  = 1,
+};

zephcore/boards/nrf52840/sensecap_solar/sensecap_solar_nrf52840.dts

@@ -91,7 +91,7 @@
 	zephyr,user {
 		io-channels = <&adc 7>;
 		/* Zephyr: ADC_GAIN_1_6 + ADC_REF_INTERNAL = 3600mV full-scale; 1:3 voltage divider → 3600*3 */
-		vbat-mv-multiplier = <10800>;
+		vbat-mv-multiplier = <10854>;  /* 3:1 divider, 3.6V ref; +0.5% for nRF SAADC gain error */
 	};
 
 	aliases {

zephcore/boards/nrf52840/t1000_e/battery_curve.c

@@ -0,0 +1,25 @@
+/*
+ * SPDX-License-Identifier: Apache-2.0
+ *
+ * T1000-E single-cell LiPo OCV curve — 21 points at 5% steps.
+ * 11-point base linearly interpolated to 5% resolution.
+ * Index 0 = 100% (4190 mV), index 20 = 0% (3100 mV).
+ *
+ * Notable shape: very flat plateau 3.72–3.82 V, steep cliff below 3.64 V.
+ */
+
+#include "battery_curve.h"
+
+static const uint16_t ocv_t1000_e[21] = {
+	4190, 4116, 4042, 3999, 3957, /* 100 .. 80% */
+	3921, 3885, 3852, 3820, 3798, /*  75 .. 55% */
+	3776, 3761, 3746, 3735, 3725, /*  50 .. 30% */
+	3710, 3696, 3670, 3644, 3372, /*  25 ..  5% */
+	3100,                          /*   0%       */
+};
+
+const battery_curve_t battery_curve_default = {
+	.ocv_mv     = ocv_t1000_e,
+	.num_points = 21,
+	.num_cells  = 1,
+};

zephcore/boards/nrf52840/t1000_e/t1000_e_nrf52840.dts

@@ -102,7 +102,7 @@
 	/* Battery ADC channel reference for ZephyrBoard */
 	zephyr,user {
 		io-channels = <&adc 0>;
-		vbat-mv-multiplier = <7200>;  /* 2:1 voltage divider, 3.6V ref */
+		vbat-mv-multiplier = <7236>;  /* 2:1 divider, 3.6V ref; +0.5% for nRF SAADC gain error */
 	};
 
 	/* Buzzer on PWM0 channel 0 (P0.25) with enable on P1.05 */

zephcore/boards/nrf52840/thinknode_m1/thinknode_m1.dts

@@ -151,7 +151,7 @@
 	/* 150K+150K voltage divider (2:1) on AIN2 (P0.04) */
 	zephyr,user {
 		io-channels = <&adc 2>;
-		vbat-mv-multiplier = <7200>;
+		vbat-mv-multiplier = <7236>;  /* 2:1 divider, 3.6V ref; +0.5% for nRF SAADC gain error */
 	};
 
 	/* ---- Buzzer on PWM0 ---- */

zephcore/boards/nrf52840/thinknode_m3/thinknode_m3.dts

@@ -96,7 +96,7 @@
 	 * With GAIN_1_6 + internal ref (3600mV full scale) × 2 = 7200 multiplier. */
 	zephyr,user {
 		io-channels = <&adc 3>;
-		vbat-mv-multiplier = <7200>;
+		vbat-mv-multiplier = <7236>;  /* 2:1 divider, 3.6V ref; +0.5% for nRF SAADC gain error */
 	};
 
 	/* Buzzer on PWM0 channel 0 (P0.23, PIN_BUZZER=23) */

zephcore/boards/nrf52840/thinknode_m6/battery_curve.c

@@ -0,0 +1,26 @@
+/*
+ * SPDX-License-Identifier: Apache-2.0
+ *
+ * ThinkNode M6 single-cell LiPo OCV curve — 21 points at 5% steps.
+ * 11-point base linearly interpolated to 5% resolution.
+ * Index 0 = 100% (4080 mV), index 20 = 0% (3450 mV).
+ *
+ * Notable shape: lower full-charge ceiling (4080 mV) suggesting a conservative
+ * charge termination; smooth linear discharge with no sharp cliff at the bottom.
+ */
+
+#include "battery_curve.h"
+
+static const uint16_t ocv_thinknode_m6[21] = {
+	4080, 4035, 3990, 3962, 3935, /* 100 .. 80% */
+	3907, 3880, 3852, 3825, 3797, /*  75 .. 55% */
+	3770, 3742, 3715, 3687, 3660, /*  50 .. 30% */
+	3632, 3605, 3577, 3550, 3500, /*  25 ..  5% */
+	3450,                          /*   0%       */
+};
+
+const battery_curve_t battery_curve_default = {
+	.ocv_mv     = ocv_thinknode_m6,
+	.num_points = 21,
+	.num_cells  = 1,
+};

zephcore/boards/nrf52840/thinknode_m6/thinknode_m6.dts

@@ -94,7 +94,7 @@
 	 * With GAIN_1_6 + internal ref (3600mV full scale) × 1.75 = 6300 multiplier. */
 	zephyr,user {
 		io-channels = <&adc 4>;
-		vbat-mv-multiplier = <6300>;
+		vbat-mv-multiplier = <6332>;  /* 1.75:1 divider, 3.6V ref; +0.5% for nRF SAADC gain error */
 	};
 
 	/* Board power enable (PIN_PWR_EN = P0.27) — must be HIGH for peripherals */

zephcore/boards/nrf52840/wio_tracker_l1/battery_curve.c

@@ -0,0 +1,29 @@
+/*
+ * SPDX-License-Identifier: Apache-2.0
+ *
+ * Wio Tracker L1 battery curve — single-cell LiPo, 21 points at 5% steps.
+ *
+ * 100% = 4190 mV: observed charge ceiling on this board after the ADC
+ * multiplier correction (vbat-mv-multiplier = 7236). Voltages above this
+ * clamp to 100% in the lookup.
+ *
+ * The discharge shape below 4190 mV follows the generic LiPo profile.
+ * Replace this table with measured discharge data for the specific cell
+ * installed if a more accurate curve is needed.
+ */
+
+#include "battery_curve.h"
+
+static const uint16_t ocv_wio_tracker_l1[21] = {
+	4190, 4120, 4050, 4020, 3990, /* 100 .. 80% */
+	3940, 3890, 3845, 3800, 3760, /*  75 .. 55% */
+	3720, 3675, 3630, 3580, 3530, /*  50 .. 30% */
+	3475, 3420, 3360, 3300, 3200, /*  25 ..  5% */
+	3100,                          /*   0%       */
+};
+
+const battery_curve_t battery_curve_default = {
+	.ocv_mv     = ocv_wio_tracker_l1,
+	.num_points = 21,
+	.num_cells  = 1,
+};

zephcore/boards/nrf52840/wio_tracker_l1/wio_tracker_l1_nrf52840.dts

@@ -126,7 +126,7 @@
 	/* Battery ADC channel reference for ZephyrBoard */
 	zephyr,user {
 		io-channels = <&adc 7>;
-		vbat-mv-multiplier = <7200>;  /* 2:1 voltage divider, 3.6V ref */
+		vbat-mv-multiplier = <7236>;  /* 2:1 divider, 3.6V ref; +0.5% for nRF SAADC gain error */
 	};
 
 	/* Buzzer on PWM0 channel 0 (P1.00) - no enable pin needed */

zephcore/helpers/CommonCLI.cpp

@@ -4,6 +4,7 @@
  */
 
 #include "CommonCLI.h"
+#include "battery_curve.h"
 #include <helpers/TxtDataHelpers.h>
 #include <helpers/AdvertDataHelpers.h>
 #include <adapters/board/ZephyrBoard.h>
@@ -507,7 +508,14 @@ void CommonCLI::handleCommand(uint32_t sender_timestamp, const char* command, ch
             if (adc_mult == 0.0f) {
                 strcpy(reply, "Error: unsupported by this board");
             } else {
-                snprintf(reply, CLI_REPLY_SIZE, "> %.3f", (double)adc_mult);
+                uint16_t mv = _board->getBattMilliVolts();
+                uint16_t target_mv = battery_curve_default.ocv_mv[0];
+                if (mv > 0) {
+                    snprintf(reply, CLI_REPLY_SIZE, "> %.3f  (%u mV, target >= %u mV for 100%%)",
+                             (double)adc_mult, mv, target_mv);
+                } else {
+                    snprintf(reply, CLI_REPLY_SIZE, "> %.3f  (no ADC reading)", (double)adc_mult);
+                }
             }
         } else if (memcmp(config, "rxduty", 6) == 0) {
             snprintf(reply, CLI_REPLY_SIZE, "> %d", (int)_prefs->rx_duty_cycle);

zephcore/helpers/battery_curve.c

@@ -0,0 +1,60 @@
+/*
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+#include "battery_curve.h"
+
+/*
+ * Generic single-cell LiPo OCV curve — 21 points at 5% steps.
+ * Derived from measured LiPo discharge data; 11-point base expanded to
+ * 21 points by linear interpolation for better knee resolution.
+ *
+ * Index 0 = 100% (4190 mV), index 20 = 0% (3100 mV).
+ * 100% is 4190 mV, not 4200 mV — reflects observed charge ceiling across
+ * multiple boards after the charger transitions to maintenance mode.
+ */
+static const uint16_t ocv_generic[21] = {
+	4190, 4120, 4050, 4020, 3990, /* 100 .. 80% */
+	3940, 3890, 3845, 3800, 3760, /*  75 .. 55% */
+	3720, 3675, 3630, 3580, 3530, /*  50 .. 30% */
+	3475, 3420, 3360, 3300, 3200, /*  25 ..  5% */
+	3100,                          /*   0%       */
+};
+
+__attribute__((weak))
+const battery_curve_t battery_curve_default = {
+	.ocv_mv     = ocv_generic,
+	.num_points = 21,
+	.num_cells  = 1,
+};
+
+uint8_t battery_curve_lookup(const battery_curve_t *curve, uint16_t mv)
+{
+	if (mv == 0) {
+		return 0;
+	}
+
+	uint16_t cell_mv = mv / curve->num_cells;
+	uint8_t  n       = curve->num_points;
+
+	if (cell_mv >= curve->ocv_mv[0]) {
+		return 100;
+	}
+	if (cell_mv <= curve->ocv_mv[n - 1]) {
+		return 0;
+	}
+
+	/* Each segment spans 100/(n-1) percent. For n=21 this is exactly 5. */
+	uint8_t seg_pct = (uint8_t)(100 / (n - 1));
+
+	for (uint8_t i = 1; i < n; i++) {
+		if (cell_mv >= curve->ocv_mv[i]) {
+			uint8_t  pct_low = (uint8_t)(100 - (uint16_t)i * 100 / (n - 1));
+			uint32_t num     = (uint32_t)(cell_mv - curve->ocv_mv[i]) * seg_pct;
+			uint16_t den     = curve->ocv_mv[i - 1] - curve->ocv_mv[i];
+			return (uint8_t)(pct_low + num / den);
+		}
+	}
+
+	return 0;
+}

zephcore/helpers/battery_curve.h

@@ -0,0 +1,27 @@
+/*
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+#pragma once
+
+#include <stdint.h>
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+typedef struct {
+	const uint16_t *ocv_mv;    /* descending — index 0 = 100%, last index = 0% */
+	uint8_t         num_points;
+	uint8_t         num_cells; /* 1 for single-cell packs (almost always 1) */
+} battery_curve_t;
+
+/* Default curve — __weak so a board-specific battery_curve.c can override it. */
+extern const battery_curve_t battery_curve_default;
+
+/* Returns 0–100 %. Returns 0 if mv == 0 (no battery / ADC absent). */
+uint8_t battery_curve_lookup(const battery_curve_t *curve, uint16_t mv);
+
+#ifdef __cplusplus
+}
+#endif

zephcore/include/mesh/Board.h

@@ -17,6 +17,7 @@ namespace mesh {
 class MainBoard {
 public:
 	virtual uint16_t getBattMilliVolts() = 0;
+	virtual uint8_t  getBattPercent() { return 0; }
 	virtual float getMCUTemperature() { return NAN; }
 	virtual bool setAdcMultiplier(float multiplier) { (void)multiplier; return false; }
 	virtual float getAdcMultiplier() const { return 0.0f; }