Warp CAN be powered by USB and the battery is not required! However… not all USB ports are made equal, and some USB ports just can’t supply enough power for Warp during certain operations.
We’ve seen this issue come up with USB 2.0 ports in particular. The max limit of USB 2.0 is typically around 500mA at 5V and sometimes the surge currents just can’t be supplied. The mode of failure varies: sometimes the board will fail an operation like an eMMC write but continue operating, other times the system might hang or reboot.
In our office, we use USB 3.0 hubs or charging ports that can supply at least 1A and they seem to all power Warp fine.
If you’re using the Interposer board, you can use two USB cables to power Warp just fine from USB 2.0. Just make sure you have the right jumpers enabled (Install the jumper for “Use Debug VBUS” & and set “WARP Battery Source” to “DCIN”). Of course you could also use the 12V DCIN but you might already be using two USB cables.
FYI when powering off battery, you won’t see these issues either. Even when connected via USB 2.0 with limited supply, the battery can help as a backup power source and allow the board to run fine.