How to Replace the Internal Battery on the Sony FX9

If you own a Sony FX9 and it's been resetting the clock every time you power it down — or throwing date and time errors on startup — the internal backup battery has reached the end of its life. It's a small lithium coin cell that runs continuously in the background to maintain the camera's clock, settings, and memory. When it dies, the camera loses its mind every time you kill the power.

The frustrating part is that this isn't a user-serviceable part by Sony's design, which means most people send it in for service and get hit with a $300–$400+ repair bill for what is, at its core, a $5 battery. We've been through this ourselves with our own FX9s, and we put together a video walking through the replacement process step by step so you can handle it without the service center.

The Battery You Need

The FX9 uses a Seiko Instruments MS621FE — a 3V, 5.5mAh lithium rechargeable coin cell. This is not the same as a standard CR2032. Make sure you order the correct part before starting. It's available through electronics suppliers and online retailers.

Symptoms of a Dead Internal Battery

If you're not sure whether this is your problem, here's what a failing internal battery looks like in practice:

Clock reset on every power cycle. The camera asks you to set the date and time each time you turn it on, even if you set it correctly the last time.

Date/time error messages on startup. The camera may display a warning that the clock battery is low or that the date and time need to be reset.

Settings loss. In some cases, user-configured settings may not persist between power cycles as the battery degrades further.

If your FX9 is showing any of these symptoms — especially if you bought it at or near launch — the internal battery is almost certainly the cause. Sony released the FX9 in late 2019, which means early adopters are now hitting the natural end-of-life window for this battery.

What the Repair Involves

This is not a simple panel removal. Getting to the internal battery board requires disassembling several sections of the camera body. The video above walks through each step in sequence. Take your time, work carefully, keep track of your screws, and don't force anything.

Key things to keep in mind before you start:

Work on a clean, well-lit surface. The FX9 has small screws and cable connections that are easy to lose or damage.

Photograph each step as you go. Before removing any panel or cable connection, take a photo so you have a reference for reassembly.

Be aware of the KSW-72 MOUNT board. In some cases — particularly on early production units — the board that houses the battery may also need replacement. If a new battery alone doesn't fix the issue, the board itself may have failed. This is less common but worth knowing before you start.

Reassembly is the reverse of disassembly. Don't rush the reconnection of ribbon cables and connectors. Seat each one fully before moving on.

Is It Worth DIY-ing?

If you're comfortable with basic electronics disassembly and have handled camera maintenance before, yes. The repair itself is straightforward once you're inside — it's getting there that takes patience. If you've never taken apart a professional camera body before, this may not be the place to start. A trusted local repair shop that works on broadcast cameras is a better option than Sony's service center if you'd rather not do it yourself — the repair should take under an hour of skilled labor.

We operate our FX9s hard — multi-camera events, conventions, live productions across Las Vegas — and keeping them maintained is part of running a professional gear fleet. If you're producing in Las Vegas and need FX9 crews or gear support, we know these cameras inside and out.