One thing to bear in mind if you do high mileages in an EV but want to charge at home rather than at a high output DC charger is the number of miles you can put on during an overnight charge.
A typical home charger is 7KW and the usual cheap overnight rate goes from Midnight to 05:00. So this gives you the ability to put in 35KWh of charge - and actually a bit less due to conversion losses.
If you bat up and down motorways at 70mph for your 300 miles, you'll probably be getting 4 miles/KWh or less, so your 35KWh will be giving you only 140 miles of range - not enough to replace 300 miles of range in a single overnight charge at the cheap rate.
So what does this mean? You may well find that it's sensible to use a high output charger on these long trips, especially as you'll be stopping for a refreshment/bio-break every couple of hours anyway - it's good to stay hydrated and refreshed on a long journey. And doing these long journeys for work means you'll be claiming back the cost so the higher price won't impact you.
A typical DC charger can bang in 150KW, and some can do up to 350KW (assuming your car can take it). So a 20 minute coffee stop will see you adding something like 200 miles of range in that time.
For those much more frequent occasions when you aren't doing 3 or 400 miles in a day, your cheap overnight charge at home will be more than adequate.
So the upshot is you might well find that monster range isn't actually that much of a requirement any way, and something in the 250 mile bracket could well suit you better, not least because it gets you a much wider choice of cars. Start the day with a full 250 mile range on board, do 200 miles, stop for a wee and a coffee, do another 200 miles, you've got your 400 mile journey done with no problem.
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