Not really, the longer it runs on battery, the more it needs to recharge from the gas engine.
Here are some tips for better MPG in the RX400h:
- Keep your tire pressure at 38-40 PSI.
- Get low rolling resistance tires (LRR) if you don't have them. The OEM Michelin S8 tires are LRR (Green-X). These will add about 3 MPG to non-LRR tires.
- Turn off the A/C if possible (summer AND winter, in AUTO mode the AC is on by default at any set temp). Go to the climate screen and disable AC, and you can still keep it in AUTO without running the A/C compressor.
- Use the heat sparingly in winter. Having a high set temp will make the engine run longer, especially until the engine is warmed up (157° F and up). The heated seats can compensate for a lower cabin temp.
- Keep it under 42 mph to allow longer gliding on battery only. Feather the gas to keep it around 40 mph. Works great when the speed limit is 35 or 40. I can sometimes get up to 1-2 miles on battery only.
- A highway speed of 50-60 mph will get you MUCH better MPG than 60-80 mph. My experience in summer: 55 mph - 32 mpg, 75 mph - 26 mpg.
- Don't accelerate hard, coast as much as possible, and brake lightly to use regenerative braking instead of the friction brakes.
- Buy a ScanGauge computer so you can see the engine RPM and engine temp, so you can practice keeping it in battery only stealth mode at 0 rpm.
- Make sure to perform the ISC reset any time the 12V battery is disconnected for service or gets low on charge. The effectiveness of this is debatable but it can't hurt.