You can get foldable ebikes (e.g. a Brompton), they might be easier to store inside.

In addition to mekhos excellent comment, there is also bike insurance and some bike lock manufacturers offer “anti-theft protection” provided certain conditions are filled.

Disclaimer: I cannot vouch for any of these options, I am just informing you of their existence.

Most batteries are removable for safety, anti-theft, and maintenance purposes. Pick a bike that requires a key to remove battery (they can account for ~40% of the cost of the bike) then take it upstairs/into work to keep it charged.