^ This. Also, in my experience, the biggest battery drain isnt the lights themselves but how the board handles sleep mode. Ive spent years hunting for a setup that doesnt need a cable every third night and over the years ive learned that most manufacturers lie about battery life by testing with the LEDs off. If you can stretch that budget slightly or find a sale, these have been the most reliable for me long-term:

• ASUS ROG Falchion Wireless 65% Mechanical Gaming Keyboard. This one is a beast. It has a side touch panel that lets you adjust brightness on the fly without diving into menus. Battery lasts weeks if you keep the RGB at about 30 percent, which is plenty for dark rooms.
• Razer BlackWidow V3 Mini HyperSpeed Wireless 65% Mechanical Gaming Keyboard. I picked this up recently for right around 100 bucks. The software is kinda annoying but the lighting profiles are very granular. You can set a super aggressive timer to kill the lights after 60 seconds of inactivity which saves tons of juice. The key is really just setting that auto-sleep to be fast... most people forget that and wonder why the board is dead in the morning.

Get the renewed Logitech MX Mechanical, around $100: https://www.amazon.com/Logitech-Mechanical-Illuminated-Performance-Bluetooth/dp/B0B836YG1P?------123456890?7649-20&th=1

If you're looking for something more budget-friendly, check out the Corsair K65 Plus Wireless. It's a mechanical keyboard with decent RGB backlighting and the build quality is solid. The wireless connection has been rock solid for me, no lag issues during gaming or typing. Only downside is it's a bit bulky compared to some other options.

Totally agree with the point about software customization—it’s the most overlooked part of battery life. If the firmware doesn't handle sleep states or auto-dimming correctly, the RGB will kill your board in 48 hours. I've been testing wireless boards for years, and long-term, you really want something with a beefy battery and efficient 2.4GHz polling. Here are two options I've used extensively that hit that $100 sweet spot: 1. NuPhy Air75 V2: This is my current daily driver. It has a massive 4000mAh battery which is basically double what most boards in this price range offer. Since it supports QMK/VIA, you can precisely map your brightness layers and sleep timers. Tbh, the build quality is top-tier for a low-profile board. 2. Razer BlackWidow V3 Mini HyperSpeed: Don't sleep on this one if you find it on sale. Razer's HyperSpeed wireless protocol is surprisingly power-efficient. In my experience, the battery management is very aggressive (in a good way) and the shine-through on the keycaps is much better for late-night visibility than the side-lit options. Basically, if you want the best longevity, look for a board with at least a 3500mAh battery and stick to 2.4GHz instead of Bluetooth whenever possible. It's much more stable and usually more efficient at maintaining a connection.

Nice, didn't know that

If you're looking for a wireless keyboard with excellent backlighting and solid battery life, the Keychron K6 is a fantastic option to consider. It’s a compact 65% mechanical keyboard that offers customizable RGB backlighting with adjustable brightness levels, perfect for late-night work sessions. The Keychron K6 is compatible with both Windows and macOS, and it supports Bluetooth connectivity for up to three devices, making it versatile for multi-device setups.

Just want to mention - make sure whatever you get has good software for customizing the backlighting. Nothing worse than having lights that are too bright for night use or can't be adjusted properly. I learned this the hard way with a cheaper model that had fixed brightness levels.

I'll throw in a suggestion for the Apple Magic Keyboard if you're in the Apple ecosystem. Clean design, great build quality, and the backlighting is subtle but effective. Battery lasts forever and the low-profile keys are surprisingly comfortable once you get used to them. Obviously works best with Macs but functions fine with Windows too.