I think even these estimates of Toyotas battery capacity are too high. Here's my attempt:

Prius Prime PHEV: 8.8 kWh Regular Prius: I couldn't find recent numbers, but 1st gen was 1.2 kWh

All other hybrids seem to have between 1-2 kWh https://en.wikipedia.org/wiki/Hybrid_Synergy_Drive#High_volt...

European PHEV sales were 0.3% of all sales and 0.65% of all hybrids [1]

US Prius Prime 2017 sales (I think their only PHEV model) were 21k units. [2] Note that 21k units just in the US out of 1.5m hybrids total gives us 1.4%, so maybe the PHEV prius is not selling as well in Europe.

Let's say we have the following scenarios of 2.5 or 5% of the total 1.5m number being PHEV to be conservative. Further assume that regular hybrids have 1.5 kWh. For the 2.5% scenario, if my math is correct, that yields 550,000 kWh. For the 5% PHEV scenario, that yields 874,000 kWh.

[1] https://insideevs.com/only-0-3-of-toyota-sales-in-europe-wer... [2] 2017 table from https://insideevs.com/monthly-plug-in-sales-scorecard/