That has been the elephant in the room since the first dreams of all electric car fleet. I have not seen a proposal (or even commentary on) how governments will deal with this. I doubt they can tax electricity in such an easy manner (even in energy equivalents). In Germany the tax is roughly ~50 cents on a liter of gasoline + 19% on top of that VAT + (German) emission tax (for modern diesel 300 Eur/year/car). Thats on the order of 10(s) billion in a year to the federal government from CE cars.
Governments shouldn't even consider taxing electrics. Trucks create the majority of road damage (https://www.insidescience.org/news/how-much-damage-do-heavy-...). Trucking companies should pay for the roads along with gas powered vehicles and if that gets prohibitively expensive then get an electric car or send goods primarily by rail. This is the real challenge of fighting climate change, many powerful and wealthy classes of people and businesses are going to have to pay for more of their share of their negative externalities.
Basically road pavement damage is proportional to weight of vehicles that run over them (and - to a lesser extent - to the amount of vehicles).
Having more electric vehicles actually increases - on average - the weight of cars, and - indirectly - road damage (how much is to be seen in practice).
For commercial fleets, trucks are already so heavy that - as you say - provoke the most damage, but they are heavy because they move things that "you/we" need or want, and that "you/we" actually pay for in the end.
So, if there won't be any more income from gas-guzzling cars, and taxing the electric cars is politically not viable, what remains is that the costs will be put on comnmercial transport, which means ultimately that final users will pay more, much more for transport of the goods they buy.
The traditional approach was to tax indirectly (via car related taxes) the - in theory - more affluent part of the population (that could afford to buy and maintain a car), if this source of income ceases to exist, the only way to replace it is to tax more "what remains".
It's more revenue friendly to have a yearly road tax than to tax registrations for a few reasons -
1. You don't disincentivize new car purposes (it's important to buy new cars to replace the old polluting ones you want off the road and it's good for the economy),
2. Your tax receipts aren't stable (if you tax registrations your tax revenue pro-cyclical - when the economy crashes and you need to pay higher unemployment and other benefits you also see a drop in tax revenue),
3. Recurring taxes allow you to make smaller changes over longer periods of time without influencing behaviour.
4. The tax revenue from a £54k Landrover Discovery in the UK for example is around £1,300 a year - if you want to get the same revenue from a registration that tax would enormous.
