This information pertains to LabQuest 2.
If you have LabQuest 3, see this article.
The original LabQuest does not support this functionality.
In LabQuest OS version 2.2 and higher, in the System Information dialog (tap on the Home icon, select System, and then System Information,) there is a Battery tab that provides information from the battery controller chip to the user.
| Field | Units | Notes |
| acpg | Has AC power? 1=yes, 0=no. The LabQuest can’t tell the difference between a charging station and an AC adapter, they both work equally well. | |
| chg_st | Battery Charging? 2=charging, 3=discharging. The reference to “Sleep mode” you see when it is discharging means that the battery monitoring chip is trying to conserve power, it doesn’t mean the LabQuest is asleep. | |
| AtRate | We don’t use this field on the LabQuest. AtRate is a settable field, useful for guessing future power consumption. | |
| AtRateTimeToEmpty | We don’t use this field on the LabQuest. AtRateTimeToEmpty gives a number based on the capacity and loading curve related to the AtRate field value.) | |
| Temperature | Degrees C | This is used for figuring out if the battery is malfunctioning. The calibration is approximate. |
| Voltage | mV | A full battery is around 4200, an empty battery is close to 3000. Numbers below that generally mean a failed battery. |
| Flags | This field is a collection of values from binary registers, indicating the mode the monitoring chip is operating in and reporting error states. | |
| NominalAvailableCapacity | mAh | Remaining battery capacity, assuming that it is discharged at an ideal rate/temperature/etc. The biggest assumptions are: 20 hour constant current rate, 25 degrees C. |
| FullAvailableCapacity | mAh | The capacity of this battery when fully charged, assuming ideal conditions. For a new battery this will typically be in the 3600 range, and will go down as the battery ages. |
| RemainingCapacity | mAh | Remaining battery capacity when compensated for the discharge/temperature/etc curve it is actually running on. |
| FullChargeCapacity | mAh | Capacity when fully charged, compensated for the discharge curve in the real conditions. |
| AverageCurrent | mA | Averaged over 1 second so not to report surges. Negative when discharging, positive when charging. |
| TimeToEmpty | minutes | This assumes that current doesn’t change, but that is usually a bad assumption: if you have the screen set to turn off after inactivity, TimeToEmpty will be read too low when the screen is turned on and you are reading the value (the battery will last longer than that.) See also: TimeToEmptyAtConstantPower. If you are charging TimeToEmpty will say 65535. |
| TimeToFull | minutes | If you are running on battery TimeToFull will say 65535. |
| StandbyCurrent | mA | Amount of current used if you put the LabQuest to sleep, (short press of the power button.) |
| StandbyTimeToEmpty | minutes | This is how long the LabQuest will last in sleep before it shuts off (1440 minutes/day: typically this number is several weeks). |
| MaxLoadCurrent | mA | Maximum load ever seen by the battery. If you’ve ever used a high current draw sensors/USB devices, this number will be higher. |
| MaxLoadTimeToEmpty | minutes | The time the unit will last if you use the maximum load continually. |
| AvailableEnergy | mWh | Because voltage falls as the battery discharges, this isn’t as simple as multiplying Capacity*Voltage. For a new fully charged battery this will be around 12210, (as printed on the front of the battery.) |
| AveragePower | mW | Note there is an integer overflow problem here: when charging this reads mW like it should, but when discharging it adds 65536 to the (negative) number. |
| TimeToEmptyAtConstantPower | minutes | Some of the components in the LabQuest need a stable power supply voltage, (for instance, sensors need 5 volts,) and as such the voltage regulator supplying those components will draw more current as the battery discharges and the voltage falls, resulting in a constant power draw. Other components, (most of the hardware inside the device,) run fine in the entire range of battery voltages, so current stays the same as the voltage drops, (so the power decreases.) This number assumes that all components are constant power where as TimeToEmpty assumes constant current. The actual time the battery will last is somewhere between the two: closer to TimeToEmpty if you don’t have heavy current drawing probes, closer the TimeToEmptyAtConstantPower if you are using multiple heavy current draw probes like the CO2 sensor, Ethanol sensor, or the Motion Detector. |
| CycleCount | count | Number of charge/discharge cycles the battery has seen. This value is reset to 0 by certain software updates so it may be low. |
| StateOfCharge | % | Percentage full. |
Some software updates, (all of the LabQuest 2 updates as of this writing, including the 2.2 update,) rewrite the battery monitoring chip’s firmware with updated values. This has a result of resetting a lot of the capacity values back to defaults, and the monitoring chip then has to remeasure those values over a couple charge/discharge cycles. The side effect of this is that for a few days after performing an update the battery gauge will be wrong, (for instance, it may report 60% full when it is really 40% full,) and the TimeToEmpty/TimeToFull values will also be wrong.
In LabQuest OS 2.0-2.0.2, the LabQuest turns off when the battery monitor says only 2% is remaining, (due to a bug in 2.0.1, this usually meant that the LabQuest would crash before it shutdown.) In version 2.1, it shuts down when the battery monitor says 2% is remaining, or the voltage measured on the motherboard reached critical values and it is danger of crashing. It version 2.2, the LabQuest only shuts down when the voltages reach critical values, regardless of what the battery gauge says. As such, the battery gauge sometimes will say that the battery has been empty for hours yet the LabQuest will continue to function; as you do more charge-discharge cycles the gauge should become more accurate.
USB Charging
The LabQuest 2 can charge over USB when connected to a computer, when this happens acpq will still read 0 like it is running on battery, but chg_st will be 2, like it is charging. However, depending on the power usage of the LabQuest itself, it may or may not actually be charging. The USB specification only allows a device to draw a certain amount of power from a computer, and with WiFi turned on and the screen set to full brightness the LabQuest uses more power than it gets from the computer so the LabQuest will discharge, (although much slower than if it isn’t connected to the USB power.) To tell if the battery is actually charging, look at the number for AverageCurrent, a positive value means it is charging. The LabQuest doesn’t charge over USB when turned off or asleep, and won’t charge from a USB outlet, (like a phone charger,) it will only charge from an enumerated USB port like on a computer, (Logger Pro doesn’t have to be running.) With the screen set to turn off when idle and no sensors attached, the LabQuest will take a more than a day to go from empty to full over USB. Note that the LabQuest will charge from its AC adapter/charging station when off, asleep, or turned on, it takes about 8 hours to get a full charge regardless.
Other devices (phones and tablets) that charge via USB cables have additional hardware on the USB port to detect when it is connected to a USB power outlet vs a computer USB port: for instance an iPad won’t charge at all on a USB 1.1-2.0 port when the screen is turned on, will charge very slowly on a USB 3.0 port, (3.0 has more power,) and charges best from an AC adapter.