By design, the TDP slider on the Steam Deck will put a hard limit on how much power the CPU/GPU can draw from the battery. You can't get much more direct battery savings than that.

Valve has already issued a fix for a Steam client update that caused boot loops and broke TDP and GPU clock speed sliders. Valve led a bad patch through beta, but fixed it fast. Skip to main content ...

Valve's Steam Deck has introduced a whole new crowd to PC gaming, and much like a full-fledged desktop or laptop, you can customize it to suit your tastes.

With the improved thermal potential unlocked by the water-cooling loop, the modder overclocked the Steam Deck using a patching tool to push the Steam Deck's TDP from a stock 15W to 27W.

STEAM DECK SETTINGS; TDP: 10W; FSR: On (if plugged in or docked) I found that mostly sticking to Medium graphics settings rather than the High or Ultra ones allowed Fallout 4 to run more smoothly ...

On the other side, the Steam Deck OLED operates at a consistent TDP of 15W. You might think that the lower power would mean lower performance, but our tests showed something quite interesting.

The Steam Deck OLED has a better screen, battery life, and Wi-Fi module. But power-wise, it’s identical to the original. Running a game on the Steam Deck OLED will be the same as on the Steam Deck.