Tesla (NASDAQ:TSLA) issued a Jan. 30 fourth-quarter update packed with information. The shareholder letter gave investors insight into Tesla's newfound profitability and its product plans for the Model Y, Tesla Semi, and a fully electric pickup truck, among other things.

But for investors to get a full grasp of the company's business, they'll need to do more than digest the headline takeaways from Tesla's quarterly update. Given the company's rapid growth and its quickly evolving business dynamics, investors may want to read over the company's entire fourth-quarter shareholder letter.

To this end, here are three additional tidbits from the letter that could easily be overlooked, but are crucial to the California-based company's ongoing expansion.

Model 3 interior and 15-inch touch display

The view from the Model 3. Image source: Tesla.

1. Tesla's Model 3 gross margin was greater than 20%

As Tesla has increased Model 3 production and deliveries, the vehicle's gross margin (gross profit as a percentage of sales) has improved at an astounding rate, swinging from a negative gross margin in the first quarter of 2018 to greater than 20% by the third quarter of last year.

Some investors have worried that the new vehicle's gross margin would narrow as Tesla introduces lower-priced variants. Fortunately, this hasn't been the case.

"Despite introducing a lower-priced mid-range variant and other headwinds, Model 3's gross margin remained stable in Q4 at over 20%," Tesla said in its fourth-quarter update.

The fact that Tesla was able to maintain a gross margin for the vehicle above 20% in Q4 despite introducing a lower-priced version demonstrates how economies of scale are helping lower costs on a per-unit basis. Tesla delivered 63,359 Model 3 units in Q4, up from just over 56,000 in Q3; growing Model 3 deliveries throughout 2018 has helped Tesla reduce fixed costs, labor hours, and scrap rates per unit produced. 

What's important is that this scalability of Model 3 production bodes well for Tesla's aggressive efforts to move closer to its promised $35,000 version of the vehicle for a launch later this year.

2. Tesla's energy storage business is booming

It's easy to overlook Tesla's fast-growing energy business. Of course, there's not too much harm in doing this since the segment accounted for just 7% of revenue last year. But totally ignoring Tesla's energy business -- particularly its energy storage unit -- would be a mistake. Because Tesla's energy storage sales are soaring.

"In 2018, we deployed 1.04 [gigawatt-hours] of energy storage, nearly tripling our energy storage deployments compared to 358 [megawatt-hours] deployed in 2017," Tesla said. Even more, the company expects strong momentum in energy storage deployments to continue in 2019. "With a better supply of cells and new manufacturing equipment, we are aiming to more than double energy storage deployments to over 2 GWh in 2019," the company said.

Check out the latest Tesla earnings call transcript.

3. Expect an improved Model 3 production rate

Investors should realize that Tesla plans more upside to Model 3 production capacity at its factory in Fremont, California.

"Model 3 production volumes in Fremont should gradually continue to grow throughout 2019 and reach a sustained rate of 7,000 units per week by the end of the year," Tesla said. This is up from an average production rate of about 4,700 units per week in the fourth quarter of 2018. Management also noted that it plans to "produce Model 3 vehicles at maximum production rates throughout 2019," suggesting Tesla believes it will have plenty of demand throughout the year for a growing number of deliveries.