I bought my Model S for many reasons, but battery efficiency was not one of them. The question of whether Tesla has the best battery technology or not has been nagging at me since i’ve been learning more about Tesla and EVs in general. I set out to try to answer that question and was surprised with what I found.

Initial Comparison

I started by making a list of only 100% electric cars, what people call Battery Electric Vehicles (BEVs). I wanted to cut out the hybrids and other types as their batteries would be smaller and they would be less dependent on the quality of the battery. I ended up with 10 cars in my list. All the cars in the list use Lithium-ion batteries as they’re reportedly the highest energy and power density combined of any energy-storage medium. Each vendor uses various tricks to get their best efficiency including how they lay out the batteries, how they heat/cool them, how they set min/max charge levels, etc. 

Next I used a number of online sources to collect the basic information on battery size, EPA range, MPGe rating,  max charge rate, etc. I came up with the following table:

 Note: the RAV4 EV had a Tesla-provided battery pack. The car and pack arrangement have ended production.

Initial analysis

One thing that immediately jumps out is that all the range per kWh results look somewhat similar. The worst is the RAV-4 but the others are all within 30% of the best — the Tesla Roadster. Second place in this efficiency measurement is the Smart Electric Drive. Some other things stand out from this data:

• The Tesla Roadster, with its low weight and relatively large battery, is much more efficient than the Model S and was the most efficient car in this group.
• Second place in miles/kWh is the Smart Electric Drive. Another low weight small car — Smaller, lighter cars lead the pack on miles/kWh efficiency.
• No surprise to anyone, the Tesla’s all have the largest batteries and furthest range of any EV.
• Also not a surprise, battery size directly correlates with range.
• The Model S is not the most efficient car in terms of converting kWh to miles driven.
• The Model S is also not the most efficient car in terms of MPGe ratings.
• The larger the battery, the larger the charge rate the vendor seems (needs?) to support.
• Tesla has the largest battery packs on the market, at least 2x any competitor.

From this data it seems perhaps Tesla has an edge in size and/or charge rate but not efficiency the way its measured here. But I suspected there was more to it than this and I wanted to dig deeper so I expanded my research to add some more data.

Perhaps Tesla has the technology edge only in size and/or charge rate

Expanded Comparison

There are some things that weren’t factored into the earlier data. Like how many people or how much cargo you’re able to move with those kWh. You can make an extremely efficient electric bike but its not very practical for moving your family around or hauling groceries. What does the data look like if you try to account for weight or cargo capacity?

 With this additional data we start to see different leaders. The larger batteries add a lot of extra weight of their own, but still, the Model S is more efficient at moving a pound of weight over a mile per kWh than any other EV. Other vendors aren’t too far off with the Ford Focus Electric in second place followed closely by the Mercedes B-Class.

The Model S is more efficient at moving a pound of weight over a mile per kWh than any other EV, but not by a huge margin.

Moving weight around is nice, but that needs to translate into utility. Looking at how efficiently the EVs move a cubic foot of cargo space Tesla also comes out on top. Interestingly, in every efficiency category I found the 60kWh Model S beats the 85 kWh Model S. Like weight, some competitors are not far behind like the Mercedes B-Class at 71 vs 98 for the Model S 85.

The Model S is also the most efficient at moving cubic feet of cargo capacity per kWh/mile than any other EV, again not by a large margin.

Summary

Collecting the data and reviewing it took longer than I would have liked. In raw efficiency terms the Model S doesn’t have an edge on competition. When you factor in utility you can see a bit of an edge in the Model S, but that utility alone is not likely going to justify the price difference between the Model S and the close competitors.

From the data, my main conclusion around battery technology is that for the Model S, battery size (and range) is the key differentiator by the largest factor. This may not accurately reflect the difficulty and intellectual property around building batteries that are >2x larger than the competition or supporting the necessary higher charge rates, physical layouts, etc but it is what is visible to the consumer. There also could be huge business benefits in terms of costs in choosing to go with special packaging for 7,000 Panasonic batteries vs building a specialized battery pack that we’re not able to get data for.

Personally, I bought the Model S because it is the only EV currently on the market that can handle my mileage. The EPA ranges you see above and often quoted are under pretty ideal conditions. Add some cold weather in, drive a bit faster than 55 MPH, or otherwise change those calculated factors and your actual range limit could be quite a bit lower than the numbers quoted. The discontinued RAV-4 EV was the closest competitor by a decent margin and that couldn’t do my normal day of 100 miles round trip commuting. The others are much further off.

The Model S isn’t the most efficient EV on the market, but for some people range is king. For those that don’t need the range, it’s going to come down to picking an EV that can comfortably handle their needed range and fits their style. One thing that Tesla has done very well is deliver a complete package — competitive battery technology, a nicely styled car, leading driver interfaces, etc. That all comes at a price that is difficult to justify if you’re moving to an EV to save money alone, but sometimes the total is more than the sum of the parts.

The Model S isn’t the most efficient EV, but it provides the most range and utility in the EV market.