Battery

Robot Operation

• DO NOT plug/unplug battery while either power switch is in the on position.
• DO NOT attempt to power the robot with a discharged battery.
• DO NOT leave battery plugged into robot overnight or when not in use to prevent over accidental over discharge.

Charger Operation

LED Pattern	Meaning
Red/Green Flashing	BMS Connected; Battery Terminals Disconnected
Quick Red Flashing	Charge Cycle Beginning
Solid Red	Constant Current (SoC < 85%)
Red Flashing	Constant Voltage (SoC > 85%)
Solid Yellow	Equalize Stage
Solid Green	Charge Cycle Done/No Battery Connected

• When disconnecting the battery from the charger, ALWAYS disconnect the data cable first then the power cable.
• DO NOT unplug the power cable if charger indicator is not green.
• DO NOT use any charger other than the one provided with Cassie.
• DO charge in an open and well ventilated area away from bystanders.

Battery Damage Guidelines

Battery damage includes, but is not limited to:

• Short circuit
• Drop, crush, shock, vibration, or piercing
• Temperature in excess of 60 C°
• Exposure to fire or submersion in water

If a battery begins venting or catches on fire, evacuate the area and call the fire department.

Battery fires can be extinguished using a class ABC extinguisher. DO NOT use a Class D extinguisher as these are meant to extinguish Lithium metal fires and will not be effective.

Best Practices

In order to prolong your battery life, please refer to the following tips.

• Depth of discharge is an important factor in the cycle life of your battery. Repeated deep cycles to 0% will negatively impact the lifetime of your pack, as will repeated shallow cycles to above 90%.
• Storing your batteries at or below room temperature will limit self discharge and increase cycle life.
• Your battery will lose charge per day from powering the battery management circuitry, so exercise caution storing batteries for extended periods. A fully discharged battery that is stored for more than a few days, or a fully charged battery stored for long periods may be unrecoverable. For this reason it is very important that you check the charge of stored batteries approximately once per week.
• Leaving the battery plugged into the charger will not keep the battery "topped off." To charge the battery, it must be unplugged and plugged back into the charger.
  • Batteries should be unplugged from the charger when fully charged. Because of leakage current through the charger, self-discharge will increase while it remains plugged in and "shelf-life" will significantly decrease.

We recommend as best practice to have a sign out sheet for each battery you have where the state of charge and date is recorded each time a battery is used. Then when a battery is discharged below 50% it is placed on the charger, and when it has been longer than a week or so since it was used, the battery charge is checked and charged accordingly. Below are links to example policies and sign out sheets. We have also included a safety reminder sheet that summarizes the important safety and battery health policies from this page. We recommend posting this reminder near where you store your batteries.

Battery Storage Policy

Battery Checkout Sheet

Battery Safety Reminder

ESD Precautions

There is a chance that Electrostatic Discharge (ESD) will damage the PCB inside the battery. To reduce the risk of damage to your pack, take the following precautions when handling your battery:

• Before handling the battery, ground yourself by touching a large metal object, such as a desk, metal door frame, or the metal chassis of a device that is plugged into the wall.
• When plugging the battery into the robot or charger, always plug in the large 48V power connector first, and the small data cable second. This allows the ground levels to equalize before connecting sensitive components

Checking Status

Script Installation

The scripts are stored as .zip files containing the .exe and all other required files for the script to run. Extract all of the files and run the .exe file in place to execute the script. You may get a notification stating that Windows is protecting your PC by not allowing the script to run, but clicking "more info" presents the option to "Run anyway".

Download Link: bms-status-checker.zip

Prototype GUI Battery Logger

Another option for battery logging and status checking is the gui script linked below. This script has built-in log generation for tracking battery charge when batteries are checked in and out. It will also display current status of batteries in the log file. Note: This script is still in a prototype stage and may be buggy, but there is no danger to your batteries in using it.

• Executable for Linux: gui-logger-linux.zip
• Executable for Windows: gui-logger-windows.zip
• README: README.md

Script Usage

The BMSStatusChecker script presents information about the current battery state. Plug the BMS into your computer using the provided USB->Serial cable and run the script. After you select the appropriate COM port, the script will measure the voltage of each series cell group in the battery and report minimum, maximum, average and standard deviation of the cell voltages. It will also report the state of charge estimation, pack voltage, percent imbalance of the pack, battery temperature, and current measurement.

Nominal Voltage: Cell voltage should always be between ~2.8 V and 4.2 V, for a pack voltage range of 33.6 V to 50.4 V.

⚠ CAUTION: Absolute minimum cell voltage is 2.5 V. Discharging below this value will damage the cells.

Imbalance: Some level of imbalance will occur during discharge of the pack, but this will be regulated by the BMS during charging.

State of Charge: The state of charge estimator is conservative, so at 0% the battery should be charged immediately, but there is no danger of damaging the pack.