Soldered RAM doesn't hurt battery life.

No.

RAM uses very little power compared to the screen, CPU, or even Wi-Fi. Whether it’s soldered on or in a slot, the energy draw is nearly identical. The difference is far too small to measure in real-world battery life.

The real battery killers are your display brightness, background apps, and how aggressively the CPU is throttling. Soldered RAM might make your laptop harder to upgrade, but it won’t make you run for an outlet sooner.

If you’re deciding between two laptops and one has soldered RAM, worry about the screen quality and battery capacity instead.