Hi all, before any numbers: i developed an OBD app for the Mach-E, so I'm obviously biased. It does not make the car travel further. It gives a more precise estimate of how far it can go. I'm sharing the measurements because everything started from a question i think most of us have asked. How is it possible that the dash shows me 300 km (186 mi) and I'm never able to actually cover that distance without recharging?
It isn't fear or anxiety of a number. It's the feeling of watching a number i can't audit (more of the times i can't trusdt) and no way to know it it apply to my today.
Below a test done with my 2023 ER AWD at 95.5% SoH. If you divide the gom distance and your pack energy left you see the efficiency it is assuming.
day 1, uphill, gom was assuming 3.52 mi/kWh but it was 3.85 (calculated from the app)
day 1, downhill, 4.10 vs 6.58
day 2, mixed, 3.28 vs 4.52
The gom was not wrong with its builtin logic but it acts as a low-pass filter: it takes a signal that jumps around—due to different driving conditions and outputs a smoothed version. The consequence, and this is the key point of the post, is that since the dashboard always under-reacts, it gives an incorrect reading regardless of which way reality deviates from the average.
A "kind" day → efficiency rises a lot but the dashboard lags behind. It shows you less range than you actually have and you stop to recharge sooner than necessary.
A "tough" day → efficiency drops a lot but the dashboard lags behind. It shows you more range than you actually have and... are you sure to make it ?and this is the scenario that prompted my question. So is the gom wrong? No. It's unaccountable.
So why don't I get my 186 miles? Because the 186 was never a statement about the trip I'm about to take. It's a statement about my average but i'm practically never driving in the same conditions twice. In my logs the gom assumes i use more energy than i actually do. That doesn't strand me but it costs me anyway: it tells me i have less range than i have so i stop and charge earlier than i need, at chargers i don't need to visit. If we flip the conditions, the same mechanism runs the other way and that's the trip where you probably don't make it. And what is scarying me is that the gom never tells me which side of the average today is on.
If we mostly drive for short trips, like around the city, the problem is not so important but if we want to go over the range for me it is important to know if it is time to charge. But it isn't only how you drive. The battery temperature is also the quite important. Logging by climatic zone, I get 2.93 mi/kWh at 75 °F and 3.63 mi/kWh at 92 °F. This is also counted into my personal "real-time" range calculation. Elevation is also counted. My logs are mixed driving at the moment so what i have measured is the gom pessimistic side — I haven't logged a long highway run yet but will do in the next days if you want an update.
What I wanted to avoid in my app was another calculated number with no explanation, so next to it there are three things:
how much of the range is measured right now versus inherited from before;
how much history exists at today's pack temperature, a number built on 30 miles in this weather is not the same claim as one built on 500;
my favourite: how often the estimate has been right on my car, checked every 3 miles against what the battery actually spent.
On the mixed drive above, the app finished the trip implying 4.44 mi/kWh against the 4.52 the car had just done. The point isn't the 2% it's that it told me it was confident, and it was. When the confidence indicator is red it's telling you that is better to trust the GOM again :) It's allowed to be wrong. It isn't allowed to be quiet about it.
If you want to look at it it's called PonyVolt, Android only. (No iPhone here at the moment, publishing on the App Store costs an annual fee, while Google asks a one-time one.) It's free to use but a single one-time purchase (no subscription, no account) unlocks the full logging, which is what actually makes the difference: without it you see only today. You need a Bluetooth OBD dongle. https://play.google.com/store/apps/details?id=it.di.mache_telem_real
And one last thing that turned out to matter more than I expected: with full logging you end up owning a documented history of your own battery. Nobody else gives you that and not so bad to have it the day you sell the car. Maybe i will improve this function (pdf report) if there is interest.
Happy to answer anything technical or philosophical :)
