More tweaks to nRF fuel gauge

src/fw/drivers/pmic/npm1300.c

@@ -1,3 +1,6 @@
+/* SPDX-FileCopyrightText: 2026 Core Devices LLC */
+/* SPDX-License-Identifier: Apache-2.0 */
+
 /* Because nPM1300 also has the battery monitor, we implement both the
  * pmic_* and the battery_* API here.  */
 
@@ -370,8 +373,6 @@ bool pmic_init(void) {
 
   ok &= prv_write_register(PmicRegisters_BCHARGER_BCHGVBATLOWCHARGE, 1);
 
-  ok &= prv_write_register(PmicRegisters_BCHARGER_BCHGENABLESET, 1);
-
   prv_configure_interrupts();
 
   if (!ok) {

src/fw/services/common/battery/nrf_fuel_gauge/battery_state.c

@@ -5,6 +5,7 @@
 
 #include "board/board.h"
 #include "drivers/battery.h"
+#include "drivers/pmic.h"
 #include "drivers/rtc.h"
 #include "kernel/events.h"
 #include "services/common/analytics/analytics.h"
@@ -14,7 +15,6 @@
 #include "syscall/syscall_internal.h"
 #include "system/logging.h"
 #include "system/passert.h"
-#include "util/math.h"
 #include "util/ratio.h"
 
 #ifndef RECOVERY_FW
@@ -35,9 +35,6 @@
 // TODO: Adjust sample rate based on activity periods once we have good
 // power consumption profiles
 #define BATTERY_SAMPLE_RATE_S 1
-// Use fake current data for the first N seconds to improve model accuracy
-#define FAKE_CURRENT_DURATION_S 10
-#define FAKE_CURRENT_UA 100
 
 #define LOG_MIN_SEC 30
 
@@ -58,14 +55,14 @@ static TimerID s_periodic_timer_id = TIMER_INVALID_ID;
 
 static BatteryChargeStatus s_last_chg_status;
 static uint64_t prv_ref_time;
-static uint32_t s_sample_count;
 static int32_t s_last_voltage_mv;
 static int32_t s_last_temp_mc;
 static int32_t s_analytics_last_voltage_mv;
 static uint8_t s_analytics_last_pct;
 static uint32_t s_last_tte;
 static uint32_t s_last_ttf;
 static RtcTicks s_last_log;
+static bool s_charger_enabled;
 
 #if FUEL_GAUGE_STATEFUL
 #define FUEL_GAUGE_SAVE_INTERVAL_S 300
@@ -138,6 +135,8 @@ static bool prv_load_state(void *state, size_t size) {
                           sizeof(FUEL_GAUGE_STATE_KEY), state, size);
   settings_file_close(&file);
 
+  PBL_LOG_DBG("Fuel gauge state loaded");
+
   return (ret == S_SUCCESS);
 }
 
@@ -164,6 +163,8 @@ static void prv_save_state(void) {
 
   if (ret != S_SUCCESS) {
     PBL_LOG_ERR("Failed to save fuel gauge state");
+  } else {
+    PBL_LOG_DBG("Fuel gauge state saved");
   }
 }
 #endif // MANUFACTURING_FW
@@ -264,14 +265,7 @@ static void prv_update_state(void *force_update) {
   delta = (now - prv_ref_time) / RTC_TICKS_HZ;
   prv_ref_time = now;
 
-  // Use fake current data for the first N seconds to improve model accuracy
-  int32_t current_ua = constants.i_ua;
-  if (s_sample_count < DIVIDE_CEIL(FAKE_CURRENT_DURATION_S, BATTERY_SAMPLE_RATE_S)) {
-    current_ua = FAKE_CURRENT_UA;
-    s_sample_count++;
-  }
-
-  pct = nrf_fuel_gauge_process((float)constants.v_mv / 1000.0f, (float)current_ua / 1000000.0f,
+  pct = nrf_fuel_gauge_process((float)constants.v_mv / 1000.0f, (float)constants.i_ua / 1000000.0f,
                                (float)constants.t_mc / 1000.0f, (float)delta, NULL);
 
   pct_int = (uint8_t)ceilf(pct);
@@ -302,7 +296,7 @@ static void prv_update_state(void *force_update) {
   }
 
 #if FUEL_GAUGE_STATEFUL
-  if (++s_save_counter >= FUEL_GAUGE_SAVE_INTERVAL_S) {
+  if (update || (++s_save_counter >= FUEL_GAUGE_SAVE_INTERVAL_S)) {
     s_save_counter = 0;
     prv_save_state();
   }
@@ -322,6 +316,12 @@ static void prv_update_state(void *force_update) {
     prv_battery_state_put_change_event(s_last_battery_charge_state);
     s_last_log = now;
   }
+
+  // Enable battery charging after fuel gauge state has been updated for the first time
+  if (!s_charger_enabled) {
+    s_charger_enabled = true;
+    pmic_set_charger_state(true);
+  }
 }
 
 static void prv_update_callback(void *data) {
@@ -354,7 +354,7 @@ void battery_state_init(void) {
   PBL_ASSERTN(ret == 0);
 
   parameters.v0 = (float)constants.v_mv / 1000.0f;
-  parameters.i0 = (float)FAKE_CURRENT_UA / 1000000.0f;
+  parameters.i0 = (float)constants.i_ua / 1000000.0f;
   parameters.t0 = (float)constants.t_mc / 1000.0f;
 
   s_last_voltage_mv = constants.v_mv;