How to Update Volta Firmware with a Mac for Your Storyteller Overland Van

My Volta system started cutting power at almost exactly 50% state of charge. Not a slow fade, not a low-battery warning. It just turned off, every time, right around the halfway mark, like it hit an invisible wall. I called Storyteller Overland support, and they were straight with me right away: it's a known issue. The fix is a support call with one of their techs to push a firmware update, plus a replacement Volta screen shipped out to me. Easy enough. Then they mentioned the firmware tool only runs on Windows.

I'm a developer. I own a Mac, an Apple Silicon one, and no Windows PC anywhere in the house. I figured I'd deal with that later and went ahead with the support call. It was only when I plugged the USB cable in to actually run the update that I hit the real problem: getting a Windows tool to see hardware plugged into a Mac at all. That's where VMware Fusion's device compatibility quirks on Apple Silicon showed up, and where this post actually starts.

I wasn't going to buy a PC to flash a battery monitor. Turns out you don't have to. VMware Fusion is free for personal use now, and it runs Windows 11 ARM64 well enough to talk to real hardware over USB. It just doesn't tell you that up front, and it definitely doesn't tell you about the two driver installs standing between you and a working COM port.

Setting up the Windows VM

Install VMware Fusion and create a new virtual machine. Pick Install from a Windows 11 image, and make sure you grab the ARM64 build. That's the only version that runs natively on Apple Silicon, x86 Windows will just crawl or fail to boot.

Walk through Windows setup like you would on real hardware. Give it fifteen or twenty minutes. Once you land on the desktop, go to Virtual Machine → Install VMware Tools from the Fusion menu bar. This is the part people skip and then wonder why nothing works: VMware Tools installs the drivers that let the VM talk to your Mac's hardware, including USB. Reboot when it asks.

If USB still misbehaves after that, don't assume you did something wrong. Download the latest VMware Tools ARM64 package directly from VMware and reinstall it. Older Fusion releases have shipped with an incomplete USB driver set bundled in, and reinstalling from the current package clears it up.

Getting USB passthrough right before you plug in anything

Shut the VM down completely before you touch the cable. Go to VM Settings → USB & Bluetooth and set USB Compatibility to USB 3.1. If that causes issues, drop it to 3.0. Check the box for Automatically connect new USB devices, or Fusion will just ignore the Volta cable when you plug it in.

Then check macOS itself. Go to System Settings → Privacy & Security and confirm Fusion still has permission to access USB devices. I've seen macOS silently revoke this after a system update, with no dialog, no warning, nothing. If the VM isn't seeing the device at all, this is the first thing to check, not the last.

The warning you can safely ignore

Once VMware Tools is in, open Device Manager and you'll probably see a Base System Device with a yellow exclamation mark. That's the VMCI, VMware's Virtual Machine Communication Interface, and ARM64 VMware Tools doesn't ship a driver for it because Apple Silicon doesn't need it. It's cosmetic.

Right-click it, disable it, done. Or if you want it gone from Device Manager entirely, shut the VM down, open its .vmx file in TextEdit, and add:

vmci0.present = "FALSE"

Either way, nothing about graphics, shared folders, internet, or clipboard sharing changes. This step exists purely so you stop wondering if it matters.

The driver that actually matters: FT232R USB UART

Volta's firmware tool talks to the hardware over USB-to-serial, through an FTDI chip. Plug the cable in and Windows on ARM will almost certainly show FT232R USB UART with its own warning icon. Fusion successfully passed the device through. Windows ARM64 just doesn't have the FTDI driver built in, and you have to install it in two separate stages.

First, inside the VM, go to the FTDI VCP Drivers page and grab the Windows (Universal) / ARM64 package, something named like CDM-v2.12.36.4-for-ARM64-Signed-Distributable.zip. Extract the whole thing and move the folder to the root of your C: drive. Keeping it at the root avoids path errors during install, and I lost twenty minutes to that before I figured it out.

Now install the hardware driver. Open Device Manager, right-click FT232R USB UART, choose Update driver → Browse my computer for drivers → Let me pick from a list of available drivers on my computer → Have Disk, then point it at the extracted folder and select ftdibus.inf. Click through the rest.

That clears the FT232R warning, but a new device shows up right behind it: USB Serial Port, with its own exclamation mark. Expected. Repeat the same process, this time selecting ftdiport.inf instead.

When it's done, Device Manager should show a clean entry under Ports (COM & LPT), something like USB Serial Port (COM3). No warning icon. That COM port is what the Volta firmware tool actually connects to, and until it's clean, the tool won't find your hardware no matter how many times you relaunch it.

Quick troubleshooting checklist

Symptom	Fix
VM doesn't detect the USB device at all	Check USB & Bluetooth settings for auto-connect, and check macOS's USB privacy permission for Fusion
Base System Device warning	Disable it, it's the VMCI and it's harmless
FT232R USB UART warning	Install ftdibus.inf manually
USB Serial Port warning after that	Install ftdiport.inf manually
Firmware tool can't find the COM port	Confirm Ports (COM & LPT) shows no warning icon before opening the tool

These are all specific to running Windows on ARM inside Fusion on Apple Silicon. None of it shows up on Intel Macs or a real Windows PC, which is exactly why Volta and VMware haven't documented it.

This only gets your USB connection working. It doesn't replace Storyteller Overland's actual firmware update instructions, follow those for the flash itself. And keep that extracted FTDI driver folder on the VM's C: drive. A Windows update will eventually reset the driver, and you'll want it there again without redownloading anything.

My Volta hasn't dropped power at 50% since. If you're chasing the same problem, hopefully this saves you the twenty minutes I spent staring at a ftdibus.inf file wondering why Windows wouldn't take it.

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