When General Motors (NYSE:GM) announced its all-electric Chevrolet Bolt, one of the most surprising tidbits the company shared was that the vehicle would have a 60 kilowatt-hour, or kWh, battery. For only promising "more than 200 miles of range per charge," this is a surprisingly large battery for such a small vehicle. And while electric-car maker Tesla Motors (NASDAQ:TSLA) hasn't yet said what size the battery will be that goes into its Model 3, which promises at least 215 miles of range, there's good reason to believe the battery size will be smaller than the Bolt's.

Model 3. Image source: Tesla Motors.

What Tesla has said about Model 3's battery

The newest commentary on the Model 3's battery size comes from Tesla's first-quarter earnings call earlier this month. When an analyst asked about whether the automaker would need a 75 kWh battery for the Model 3, and if the company would be able to build the vehicle for less than General Motors is building its Bolt, Tesla CEO Elon Musk responded: 

Yeah. I mean, we don't want to get into real specifics on battery pack size, but I think it's fair to say that the average battery pack size for the 3 will be less than 75 kilowatt hours. The average energy content of a 3 pack is certainly going to be less than 75. It doesn't clearly need to be anywhere near 75 to achieve the range of 215 miles.

Musk clearly wasn't willing to tell the Model 3's battery size yet:

But we don't want to get into the nitty-gritty. It's probably unwise. Yeah.

It looks like we'll have to wait until Model 3's part 2 unveil to find out the exact battery size, but given that it won't need to be "anywhere near" 75 kWh, it's likely smaller than a 60 kWh battery.

Of course, this isn't entirely surprising. Tesla was able to achieve 208 miles of EPA-rated range with a 60 kWh battery for its Model S. So, this pretty much rules out the Model 3 needing a 60 kWh battery, since the Model 3 is about 20% smaller than the Model S. This means either General Motors is understating the Bolt's range or the automaker simply wasn't able to build an EV as efficient as Tesla.

Chevrolet Bolt. Image source: Tesla Motors.

For more context, Tesla has also produced 70 and 75 kWh versions of Model S, which achieve 234 and 249 miles, respectively, with rear-wheel drive only, or 240 and 255 miles with dual-motor all-wheel drive. And don't forget: Model S is a much larger car than the Model 3.

It will ultimately come down to cost

The question is not whether the Bolt's battery is larger than the Model 3's. If General Motors still has Tesla beat on total battery pack costs, this is ultimately what matters when it comes to profitability, since batteries are the most expensive component of EVs. But Tesla is confident in this regard, too. Musk suggested economies of scale will ultimately drive battery prices, and the automaker is certain it will have GM beat on this front:

Yeah, I mean we're highly confident that it can be made profitably, and design and manufacturing and economies of scale are keys to achieving that outcome. Yeah, I think GM is not aiming for anything near the volumes that we are, and so their -- I mean despite being a big company, their economies of scale are going to be driven by whatever elements are unique in their EV. And we know for a fact that they will not get the economies of scale that we will be at for Model 3.

Maybe a smaller battery and greater economies of scale are why Tesla is selling its Model 3 for a starting price of $35,000, while the Bolt starts at $37,500.

Model 3. Image source: Tesla Motors.

If Tesla truly does start out ahead of GM with a lower battery cost for the electric-car maker's most important vehicle to date, this would be an important milestone for the smaller auto manufacturer. It would suggest that Tesla's ruthless focus on rapidly scaling sales of an all-electric lineup of vehicles is beginning to pay off.

It should be noted, however, that GM is bringing its Bolt to market one year ahead of the Model 3. The former is scheduled for a late 2016 launch, and the latter is slated for a late 2017 launch. So, perhaps GM could catch up to Tesla on battery costs (if Tesla truly is ahead) by the time the Model 3 comes around. Furthermore, it's worth emphasizing that GM is a big enough company that its profitability on the Bolt, or lack thereof, won't have a material impact on the company's business. Model 3's profitability, however, is a make-or-break strategic initiative for Tesla.