"D-E" writes:

My local station, New Cross Gate, does not have any kind of ticket
gates/oyster reader/validator. When my Oyster runs out, if I choose to renew
it online, can I travel to another station using the tube (with an expired
oyster) and then get my Oyster updated using the exit gates, or does
reloading only happen on entrance gates?

I don't know whether the upload occurs on exit, but you can upload
the new ticket up to 5 days before the old one runs out.