diff --git a/Tools/autotest/ardusub.py b/Tools/autotest/ardusub.py
index a0eb71b5dac58..5947640790b44 100644
--- a/Tools/autotest/ardusub.py
+++ b/Tools/autotest/ardusub.py
@@ -956,7 +956,7 @@ def INA3221(self):
         })
         self.reboot_sitl()
         self.set_parameters({
-            "BATT2_I2C_ADDR": 0x42,
+            "BATT2_I2C_ADDR": 0x42, # address defined in libraries/SITL/SIM_I2C.cpp
             "BATT2_I2C_BUS": 1,
             "BATT2_CHANNEL": 1,
 
@@ -975,21 +975,24 @@ def INA3221(self):
         tstart = self.get_sim_time()
         while not (seen_1 and seen_3):
             m = self.assert_receive_message('BATTERY_STATUS')
-            print(self.dump_message_verbose(m))
-            if self.get_sim_time() - tstart > 1:
-                break
-            continue
+            if self.get_sim_time() - tstart > 10:
+                # expected to take under 1 simulated second, but don't hang if
+                # e.g. the driver gets stuck
+                raise NotAchievedException("INA3221 status timeout")
             if m.id == 1:
                 self.assert_message_field_values(m, {
-                    "current_battery": 7.28 * 100,
-                })
-                # "voltages[0]": 12 * 1000,
+                    # values close to chip limits
+                    "voltages[0]": int(25 * 1000), # millivolts
+                    "current_battery": int(160 * 100), # centi-amps
+                }, epsilon=10) # allow rounding
                 seen_1 = True
+            # id 2 is the first simulated battery current/voltage
             if m.id == 3:
                 self.assert_message_field_values(m, {
-                    "current_battery": 2.24 * 100,
-                })
-                # "voltages[0]": 3.14159 * 1000,
+                    # values different from above to test channel switching
+                    "voltages[0]": int(3.14159 * 1000), # millivolts
+                    "current_battery": int(2.71828 * 100), # centi-amps
+                }, epsilon=10) # allow rounding
                 seen_3 = True
 
     def tests(self):