Finding a single, off-the-shelf product that perfectly matches all your requirements (300W, outdoor-rated, 277V input & output, lighting battery inverter) is going to be very difficult, if not impossible. Here's why and what your likely solutions are

Challenges & Why It's Uncommon:
277V Specificity

277V is a standard voltage for commercial/industrial lighting in North America. Battery inverters often focus on more common residential voltages (120V, 240V) or lower DC voltages. Going directly from DC battery voltage to 277V AC is less common in consumer-grade or even many commercial products. While 277V is very common for mains power, inverters that operate natively at that voltage while running from battery are not typically stocked.

Outdoor Rating

Combining high voltage with outdoor rating requires robust enclosure design and safety certifications (UL, etc.), increasing cost and complexity.

Low Wattage for 277V

300W is a relatively low power draw for a 277V system. Often, 277V is used for larger lighting circuits, so inverters are built to handle much higher loads. A smaller inverter for 277V might not have enough demand to justify mass production.

Lighting Specific Design

"Lighting battery inverter" sounds like you want features specific for lights (dimming, surge protection, etc.). While UPS or off-grid inverters can power lights, they may not be optimized for lighting performance in terms of dimming compatibility or dealing with LED inrush current.

Possible Solutions and Approaches

1.

Custom Solution / Modification



Contact a Manufacturer of Industrial UPS or Inverters

This is the most likely path. Companies that manufacture larger UPS (Uninterruptible Power Supply) or inverters for industrial applications might be willing to:

Modify an Existing Product

Take a higher-wattage 277V inverter and potentially derate it or customize it for your 300W requirement.

Design a Custom Solution

This will be expensive and likely require a significant minimum order quantity.

Look for Companies Specializing in Emergency Lighting

These companies might have inverters that can run at 277V.

Potential Manufacturers to Contact (start here)



Eaton

Known for power management and UPS systems.

Schneider Electric

Another major player in power and automation.

ABB

Similar to the above two.

Generac

Good for backup power solutions.

APC by Schneider Electric

More focused on smaller UPS units, but still worth checking.

Consult a Power Electronics Engineer

A qualified electrical engineer with experience in power electronics can design a custom solution or adapt existing components. They'll be able to assess the feasibility and cost.2.

Two-Stage Solution (Voltage Transformation)



Use a Battery Inverter with a Transformer



Step 1

Use a readily available outdoor-rated battery inverter that outputs a more common voltage (e.g., 120V or 240V).

Step 2

Use an outdoor-rated step-up transformer to convert the inverter's output voltage to 277V. This transformer must be rated for the power you need (300W or slightly higher).

Pros

More likely to find readily available components.

Cons

Less efficient (transformer losses), adds more components, increases cost, more complex installation.

Example Setup



Outdoor-Rated Inverter

Find a 300W+ pure sine wave inverter that is rated for outdoor use and outputs 120V or 240V.

Outdoor-Rated Transformer

Find a transformer that converts 120V or 240V (whichever your inverter outputs) to 277V. Make sure it's rated for at least 300VA (Volt-Amps), which is close to watts for a resistive load like lighting.3.

Higher Voltage Battery System



Rare but Possible

Explore battery systems designed for off-grid applications at higher voltages. Some large-scale solar energy systems might use DC voltages that are closer to 277V after inversion, although usually it is after rectification from AC. This would require a highly specialized (and likely expensive) solution.4.

Emergency Lighting Power Pack Modification



Research Emergency Lighting Power Packs

Some emergency lighting fixtures have integrated battery packs. If you find one that uses a 277V LED driver, potentially the battery pack could be modified, or used as a starting point, for a more independent inverter application. This would likely void the warranty and require significant electrical knowledge. Not generally recommended unless you are an experienced electrical engineer.

Important Considerations



Safety

Working with high voltage (277V) is extremely dangerous. Only qualified electricians should install or modify these systems. Adhere to all local electrical codes and regulations.

UL Listing / Certifications

Ensure that any equipment you use is properly certified for its intended application and environment. Look for UL or other relevant safety certifications.

Pure Sine Wave

For most modern LED lighting, you'll want a "pure sine wave" inverter. Modified sine wave inverters can cause problems with LED drivers and potentially damage them.

Inrush Current

LED lighting can have a very high inrush current when first turned on. Make sure your inverter (or the combined inverter and transformer) can handle the surge.

Efficiency

Battery inverters are not 100% efficient. Factor in losses when calculating battery capacity and runtime.

Battery Capacity

Choose a battery size appropriate for the power (300W) and desired runtime.

Consult a Professional

Seriously consider consulting with a qualified electrical engineer or a lighting specialist. They can help you assess your needs, design a safe and reliable system, and ensure compliance with codes.

In Summary:

The most realistic path is to contact manufacturers of UPS/inverters or emergency lighting systems and inquire about a custom or modified solution. The two-stage voltage transformation approach is also viable if you can find appropriately rated components. Be prepared for higher costs and potential complexity. Safety should be your top priority. Good luck! Flag for review