The right hand meter has nothing to do with the drive modes, as mentioned. The "Charge", "Eco" and "Power" parts of the meter just show you what the traction system is doing at that exact moment. You can almost think of it like a tachometer in an ICE car. You generally want to keep the meter in the "eco" blue section when driving, and honestly as close to the bottom of it as possible for maximum range.
The drive modes (Eco, Normal, Sport) are different and change the behaviour of the throttle response from "dragging an anchor through treacle" on one end through "normal" to "snappy and much increased response". You still want to keep that right hand meter in the blue if possible when driving it though.
The Eco and Sport modes also do a couple of other things that affect the range.
- Eco mode sets the fun gauge and the comfort gauge to zero - it deadens the throttle response and it crucially shuts off the climate system so you get no AC in the summer and no heat in the winter. It also limits the power output of the motor. In my opinion this mode is for extreme emergencies only and should be avoided under normal conditions although other posters on here swear by using it. I never need the extra efficiency during commuting and if I am doing an extended range drive then I just drive a little slower to push the range out rather than shutting off all the creature comforts. YMMV.
- Normal mode is how the car was originally tuned - the throttle response is standard, so it will pull more like a traditional car with a slight delay to make it feel a bit like an ICE vehicle. The climate system will run in this mode. I do 95% of my driving in this mode, including long range trips. In this mode the car will only actively heat the traction battery if the power demand on it remains high for several seconds and the traction pack is otherwise cold.
- Sport mode improves the throttle response to make it much more like a sporty EV. The pull is immediate and it ramps to high power output very quickly. This mode also turns on the traction battery heating system right away, regardless of power demand so this will hurt your range in the winter since there's no need to heat the pack to optimum temperature for sporty driving if you're just cruising around. What it will allow you to do is to effectively pre-heat the battery to optimum temperature for rapid charging if it's especially cold.
On the 2019 and 2020 e208 the drive mode always reset to Normal when you switched the car off and you had to select it every time. I believe they changed this behaviour with the 22 model (maybe?) that it was meant to remember the last setting it was in and start back up in this mode. I'm not sure if this is true.
Either way, the mode it's in is spelled out in the dash where the speed is. The power meter on the right will always remain the same, except it gets trimmed with an accent colour in Sport mode.
By far the best way to improve the efficiency when cruising on the motorway is simply to slow down a little. If you can keep the efficiency meter as close to the bottom of the blue "eco" segment as possible you'll maximise your range far more than if you just put the car in the Eco drive mode.
Whether the car is in Eco mode or Normal mode, if you are driving at 70 mph on the motorway the energy consumption from the traction system will be the same. The only thing Eco saves you here is the power to run the climate system, which is relatively small compared to the energy used to move the car forwards. Cutting to 55-60 mph will save you
much more energy and you won't have to wear wooly mittens and a hat.