I expect the first generation of electric transport aircraft to be optimized for turboprop like speeds and similar cruising altitudes.
Such aircraft should be a little bit on the heavy side, so they won't be able to exceed 30k ft, specially considering the battery mass is fixed.
Once battery energy density improves substantially, say 100% to 150% better than today, it should be possible to design a transport aircraft optimized for ultra high altitude cruise.
Perhaps as high as FL510.
It needs a wing with a fairly large AoA range, able to achieve high subsonic mach, compensating for the very thin air by increasing AoA.
I expect such an aircraft to have at least 4 engines, perhaps up to 8.
Electric engines are simpler, using more engines with a fan like propulsion system allows for high rpm and modest fan width.
No need to have just 2 bigger engines.
If the aircraft can keep its max thrust all the way up to FL510, why not go up there ? The only limiting factor is having wings that produce enough lift.
The lithium cells used in a Tesla Model 3 have about twice the energy density of those used in the first Tesla Roadster. And the technology continues to improve.
We already have new Lithium chemistries such as Lithium CO2 being tested in labs that promise 7x the energy density of common Lithium Ion cells.
If they manage to delived just 3.5x the energy density of the best cells Tesla has today, that should be enough to produce practical 1000nm IFR range transport jets.