@@ -17,6 +17,7 @@ cd "$(dirname "$(realpath -e "${BASH_SOURCE[0]}")")"/..
 
 # Run shell tests
 cd util
+python3 test_framework_battery_extender.py
 ./test-inject-keys.sh
 
 # Run the Zephyr config tests
 
@@ -0,0 +1,351 @@
+#!/usr/bin/env python3
+# Copyright 2026 The ChromiumOS Authors
+# Use of this source code is governed by a BSD-style license that can be
+# found in the LICENSE file.
+
+"""Host regression for Framework's charge-limit command.
+
+Compile the complete production translation unit and real protocol headers.
+Mock only its EC services. No hardware or firmware flashing is involved.
+Run with: python3 util/test_framework_battery_extender.py
+Requires Python 3.8+ and a C compiler (cc, or set CC). Coverage needs GCC/gcov.
+"""
+
+import argparse
+import os
+from pathlib import Path
+import subprocess
+import sys
+import tempfile
+import unittest
+
+
+ROOT = Path(__file__).resolve().parents[1]
+SOURCE = ROOT / "zephyr/program/framework/src/battery_extender.c"
+STUB_HEADERS = (
+    "battery.h battery_smart.h board_charger.h battery_fuel_gauge.h "
+    "board_function.h charge_state.h charger.h console.h "
+    "customized_shared_memory.h extpower.h factory.h host_command.h "
+    "system.h timer.h util.h hooks.h zephyr/sys/time_units.h"
+).split()
+
+HARNESS = r"""
+#include <stdbool.h>
+#include <stdint.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include "ec_commands.h"
+#include "board_host_command.h"
+
+#define USEC_PER_SEC 1000000U
+#define SEC_PER_MIN 60U
+#define SEC_PER_HOUR 3600U
+/* Match legacy timer.h when running this regression against the baseline. */
+#define SECOND 1000000
+#define MINUTE 60000000
+#define HOUR 3600000000ULL
+#define MAX(a, b) ((a) > (b) ? (a) : (b))
+#define MIN(a, b) ((a) < (b) ? (a) : (b))
+#define EC_SUCCESS 0
+#define EC_ERROR_PARAM1 1
+#define EC_ERROR_PARAM2 2
+#define EC_ERROR_PARAM3 3
+#define EC_ERROR_PARAM_COUNT 4
+#define SYSTEM_BBRAM_IDX_CHARGE_LIMIT_MAX 0
+#define DECLARE_HOOK(...)
+#define DECLARE_HOST_COMMAND(...)
+#define DECLARE_CONSOLE_COMMAND(...)
+#define cprints(...) ((void)0)
+#define cprintf(...) ((void)0)
+
+typedef union { uint64_t val; } timestamp_t;
+struct host_cmd_handler_args {
+    const void *params;
+    void *response;
+    int response_size;
+    int version;
+};
+static uint8_t saved_limit = 80;
+static int lower = -1, upper = -1, mode;
+static uint64_t now;
+static int ac_present = 1;
+static timestamp_t get_time(void) { return (timestamp_t){ .val = now }; }
+static bool timestamp_expired(timestamp_t deadline, const timestamp_t *time)
+{ return deadline.val <= time->val; }
+static int system_get_bbram(int idx, uint8_t *value)
+{ *value = saved_limit; return 0; }
+static int system_set_bbram(int idx, uint8_t value)
+{ saved_limit = value; return 0; }
+static bool battery_sustainer_enabled(void)
+{ return lower != -1 && upper != -1; }
+static int battery_sustainer_set(int8_t lo, int8_t hi)
+{ lower = lo; upper = hi; return 0; }
+static int set_chg_ctrl_mode(enum ec_charge_control_mode value)
+{ mode = value; return 0; }
+static int factory_status(void) { return 0; }
+static int extpower_is_present(void) { return ac_present; }
+static int strtoi(const char *s, char **e, int base)
+{ return strtol(s, e, base); }
+static int parse_bool(const char *s, int *value)
+{ *value = !strcmp(s, "enable"); return 1; }
+
+#include "PRODUCTION_SOURCE"
+
+#define CHECK(condition, message) do { \
+    if (!(condition)) { fprintf(stderr, "%s\n", message); return 1; } \
+} while (0)
+
+static enum ec_status send(uint8_t operation, uint8_t limit)
+{
+    struct ec_params_ec_chg_limit_control p = {
+        .modes = operation, .max_percentage = limit
+    };
+    struct ec_response_chg_limit_control r = {0};
+    struct host_cmd_handler_args args = { .params = &p, .response = &r };
+    return cmd_charging_limit_control(&args);
+}
+
+int main(int argc, char **argv)
+{
+    extender_init();
+    batt_extender_disable = true;
+    CHECK(send(CHG_LIMIT_SET_LIMIT, 80) == EC_RES_SUCCESS, "initial SET failed");
+    CHECK(lower == 75 && upper == 80, "initial SET did not apply 75..80");
+    if (!strcmp(argv[1], "disabled")) {
+        battery_sustainer_set(-1, -1);
+        send(CHG_LIMIT_SET_LIMIT, 80);
+        CHECK(lower == 75 && upper == 80,
+              "same-limit SET left the sustainer disabled");
+    } else if (!strcmp(argv[1], "replaced")) {
+        battery_sustainer_set(90, 95);
+        send(CHG_LIMIT_SET_LIMIT, 80);
+        CHECK(lower == 75 && upper == 80,
+              "same-limit SET kept another policy's thresholds");
+    } else if (!strcmp(argv[1], "host_override")) {
+        battery_sustainer_set(-1, -1);
+        battery_extender();
+        send(CHG_LIMIT_GET_LIMIT, 0);
+        CHECK(!battery_sustainer_enabled(),
+              "timer or GET cancelled intentional host control");
+    } else if (!strncmp(argv[1], "stage", 5)) {
+        send(CHG_LIMIT_SET_LIMIT, 98);
+        batt_extender_disable = false;
+        stage = !strcmp(argv[1], "stage1") ?
+            BATT_EXTENDER_STAGE_1 : BATT_EXTENDER_STAGE_2;
+        int cap_lower = stage == BATT_EXTENDER_STAGE_1 ? 90 : 85;
+        int cap_upper = stage == BATT_EXTENDER_STAGE_1 ? 95 : 87;
+        sustainer_lower = 93;
+        sustainer_upper = 98;
+        batt_extender_deadline.val = 0;
+        batt_extender_deadline_stage2.val = 0;
+        battery_sustainer_set(cap_lower, cap_upper);
+        send(CHG_LIMIT_SET_LIMIT, 98);
+        CHECK(lower == cap_lower && upper == cap_upper,
+              "same-limit SET removed the active extender cap");
+        battery_extender();
+        CHECK(lower == cap_lower && upper == cap_upper,
+              "timer removed the active extender cap");
+    } else if (!strcmp(argv[1], "full_and_invalid")) {
+        CHECK(send(CHG_LIMIT_SET_LIMIT, 19) == EC_RES_ERROR,
+              "invalid SET was accepted");
+        CHECK(lower == 75 && upper == 80, "invalid SET changed thresholds");
+        send(CHG_LIMIT_SET_LIMIT, 100);
+        CHECK(!battery_sustainer_enabled(), "100 percent did not disable limiting");
+        send(CHG_LIMIT_SET_LIMIT, 80);
+        CHECK(lower == 75 && upper == 80, "changed-limit SET failed");
+    } else if (!strcmp(argv[1], "extender_timing")) {
+        send(CHG_LIMIT_SET_LIMIT, 100);
+        batt_extender_disable = false;
+        batt_extender_deadline.val = 1000000;
+        batt_extender_deadline_stage2.val = 2000000;
+        now = 999999;
+        battery_extender();
+        CHECK(stage == BATT_EXTENDER_STAGE_0, "stage one began early");
+        now = 1000000;
+        battery_extender();
+        CHECK(stage == BATT_EXTENDER_STAGE_1 && lower == 90 && upper == 95,
+              "stage one missed its deadline or cap");
+        now = 2000000;
+        battery_extender();
+        CHECK(stage == BATT_EXTENDER_STAGE_2 && lower == 85 && upper == 87,
+              "stage two missed its deadline or cap");
+        ac_present = 0;
+        now = reset_deadline.val;
+        battery_extender();
+        CHECK(stage == BATT_EXTENDER_STAGE_0 && !battery_sustainer_enabled(),
+              "AC absence did not reset the extender after its interval");
+    } else if (!strcmp(argv[1], "configuration")) {
+        struct ec_params_battery_extender p = {
+            .cmd = BATT_EXTENDER_WRITE_CMD, .trigger_days = 99,
+            .reset_minutes = 9999, .disable = 0
+        };
+        struct ec_response_battery_extender r = {0};
+        struct host_cmd_handler_args args = { .params = &p, .response = &r };
+        CHECK(battery_extender_hc(&args) == EC_SUCCESS, "configuration failed");
+        CHECK(battery_extender_trigger == 8553600000000ULL,
+              "99-day trigger was truncated");
+        CHECK(battery_extender_reset == 599940000000ULL,
+              "9999-minute reset was truncated");
+        p.cmd = BATT_EXTENDER_READ_CMD;
+        CHECK(battery_extender_hc(&args) == EC_SUCCESS, "readback failed");
+        CHECK(r.trigger_days == 99 && r.reset_minutes == 9999,
+              "configuration did not round-trip");
+    } else if (!strcmp(argv[1], "console_timing")) {
+        const char *args[] = { "batt_extender", "trigger", "2", "s" };
+        CHECK(cmd_parse_timestamp(4, args) == 2000000ULL,
+              "seconds changed during time-unit migration");
+        args[3] = "m";
+        CHECK(cmd_parse_timestamp(4, args) == 120000000ULL, "minutes changed");
+        args[3] = "h";
+        CHECK(cmd_parse_timestamp(4, args) == 7200000000ULL, "hours changed");
+        args[3] = "d";
+        CHECK(cmd_batt_extender(4, args) == EC_SUCCESS, "console trigger failed");
+        CHECK(battery_extender_trigger == 172800000000ULL, "days changed");
+        CHECK(cmd_batt_extender(1, args) == EC_SUCCESS, "console status failed");
+    } else if (!strcmp(argv[1], "console_controls")) {
+        const char *args[] = { "batt_extender", "enable", "2", "m" };
+        now = 123;
+        CHECK(cmd_batt_extender(2, args) == EC_SUCCESS,
+              "console enable failed");
+        CHECK(!batt_extender_disable && batt_extender_deadline.val > now,
+              "enable did not arm the extender");
+        args[1] = "timeext";
+        CHECK(cmd_batt_extender(4, args) == EC_SUCCESS, "stage-one timer failed");
+        CHECK(batt_extender_deadline.val == 120000123ULL,
+              "stage-one timer used the wrong unit");
+        args[1] = "timeext2";
+        CHECK(cmd_batt_extender(4, args) == EC_SUCCESS, "stage-two timer failed");
+        CHECK(batt_extender_deadline_stage2.val == 120000123ULL,
+              "stage-two timer used the wrong unit");
+        args[1] = "timerst";
+        CHECK(cmd_batt_extender(4, args) == EC_SUCCESS, "reset timer failed");
+        CHECK(reset_deadline.val == 120000123ULL,
+              "reset timer used the wrong unit");
+        args[1] = "reset";
+        args[3] = "h";
+        CHECK(cmd_batt_extender(4, args) == EC_SUCCESS, "reset setting failed");
+        CHECK(battery_extender_reset == 7200000000ULL,
+              "reset setting used the wrong unit");
+        args[1] = "disable";
+        CHECK(cmd_batt_extender(2, args) == EC_SUCCESS, "disable failed");
+        CHECK(batt_extender_disable && stage == BATT_EXTENDER_STAGE_0,
+              "disable did not return to stage zero");
+    } else {
+        return 2;
+    }
+    return 0;
+}
+"""
+
+
+class ChargeLimitTest(unittest.TestCase):
+    """Exercise explicit SET and the policies it must preserve."""
+
+    coverage_dir = None
+
+    @classmethod
+    def setUpClass(cls):
+        # unittest owns and closes this directory after the class finishes.
+        # pylint: disable=consider-using-with
+        temporary = tempfile.TemporaryDirectory()
+        # pylint: enable=consider-using-with
+        cls.addClassCleanup(temporary.cleanup)
+        path = Path(temporary.name)
+        for header in STUB_HEADERS:
+            (path / header).parent.mkdir(parents=True, exist_ok=True)
+            (path / header).write_text(
+                "/* EC service mocked by the host test. */\n"
+            )
+        c = path / "regression.c"
+        c.write_text(HARNESS.replace("PRODUCTION_SOURCE", SOURCE.as_posix()))
+        cls.binary = path / "regression"
+        coverage_flags = ["--coverage"] if cls.coverage_dir else []
+        subprocess.run(
+            [
+                os.environ.get("CC", "cc"),
+                "-std=gnu11",
+                "-Wall",
+                "-Werror",
+                *coverage_flags,
+                "-Wno-unused-function",
+                "-Wno-unused-variable",
+                "-I",
+                str(path),
+                "-I",
+                str(ROOT / "zephyr/program/framework/include"),
+                "-I",
+                str(ROOT / "include"),
+                str(c),
+                "-o",
+                str(cls.binary),
+            ],
+            check=True,
+        )
+        if cls.coverage_dir:
+            cls.coverage_dir.mkdir(parents=True, exist_ok=True)
+            cls.addClassCleanup(cls.export_coverage, c)
+
+    @classmethod
+    def export_coverage(cls, source):
+        """Save GCC's coverage data before the temporary files are removed."""
+        subprocess.run(
+            ["gcov", "--json-format", "--branch-probabilities", str(source)],
+            cwd=cls.coverage_dir,
+            check=True,
+        )
+
+    def check_case(self, case):
+        """Run an isolated production-code scenario and expose its assertion."""
+        result = subprocess.run(
+            [self.binary, case], capture_output=True, text=True, check=False
+        )
+        self.assertEqual(result.returncode, 0, result.stderr)
+
+    def test_same_limit_restores_disabled_sustainer(self):
+        """An explicit repeated SET must restore disabled static thresholds."""
+        self.check_case("disabled")
+
+    def test_same_limit_restores_replaced_thresholds(self):
+        """A repeated static SET must replace another policy's thresholds."""
+        self.check_case("replaced")
+
+    def test_timer_and_get_preserve_host_override(self):
+        """Readback and timer activity must not cancel intentional host control."""
+        self.check_case("host_override")
+
+    def test_same_limit_preserves_stage_one_cap(self):
+        """A repeated SET must preserve the first active extender cap."""
+        self.check_case("stage1")
+
+    def test_same_limit_preserves_stage_two_cap(self):
+        """A repeated SET must preserve the second active extender cap."""
+        self.check_case("stage2")
+
+    def test_full_charge_and_invalid_limit(self):
+        """Reject invalid limits and retain full-charge/static transitions."""
+        self.check_case("full_and_invalid")
+
+    def test_extender_deadlines_and_ac_reset(self):
+        """Keep both cap deadlines and the AC-absence reset interval."""
+        self.check_case("extender_timing")
+
+    def test_configuration_round_trips_maximum_intervals(self):
+        """Keep valid multi-day/minute intervals wider than 32 bits."""
+        self.check_case("configuration")
+
+    def test_console_time_units(self):
+        """Keep seconds, minutes, hours and days in microseconds."""
+        self.check_case("console_timing")
+
+    def test_console_enable_disable_and_timers(self):
+        """Keep public console controls and their configured intervals."""
+        self.check_case("console_controls")
+
+
+if __name__ == "__main__":
+    parser = argparse.ArgumentParser(add_help=False)
+    parser.add_argument("--coverage-dir", type=Path)
+    options, test_args = parser.parse_known_args()
+    ChargeLimitTest.coverage_dir = options.coverage_dir
+    unittest.main(argv=[sys.argv[0], *test_args], verbosity=2)