Here is a view of the amount of installed battery capacity in the 2017 automotive fleet (only looking at new cars sold in the USA this year). These numbers were estimated based on sales of the car model and the average reported size of that battery. For example, the Bolt EV was the number of Bolt EV sales times 60 KWh (actual capacity might be closer to 64 KWh, but only advertised was used). For Tesla I am doing a simple average of max and min battery sizes available, so 87.5 kwh for Model S/X and 75 kwh for Model 3 (only that model is available now). This model could be improved, but is okay for rough estimation.
Looking at the share by type of install (BEV vs PHEV) and we can see that approximately 86% of the capacity is being installed in BEVs, and most of that goes in Tesla cars.
I look at this a couple ways. If you are hitting a Lithium-ion battery cell shortage, you could make a larger impact by making more PHEVs instead of BEVs, as 5 to 10 PHEVs could be made for each Tesla. This could be researched to see if it would have a larger impact on CO2 emissions than driving a BEV. For example, if a Tesla drives 15k miles per year, but instead you could make 10 PHEVs that drive 5k EV miles a year they would amount to 50k miles fewer on gas vs the 1 Tesla driving 15k EV miles. This is only a concern when battery supply is limited.
Another way to look at this graph is it shows the percentage of the market held by Tesla. For sales volume of BEV only, it is about 40%, but for total battery capacity, it is over half of all plug in vehicles sold for 2017. This is unlikely to change in the next year with the Model 3 starting mass production, and will likely skew even more to Tesla.
The total GWh capacity of the fleet is 6.55 GWh. Tesla is aiming for 35 GWh of production at Gigafactory 1 (https://www.tesla.com/gigafactory). In other words, over 5 times the current 2017 US fleet.
Car sales figures were taken year to date from https://insideevs.com/, I have no affiliation with that site.