Create a backup of the wallet file before opening it with Electrum because it'll get updated once you opened it.
"Surprises" could occur when loading an old wallet to a new version despite of it's backward compatibility.
Having a backup ensures that you can start over whenever you need to.

Another is, load it to an offline machine and just check the balance online, in either watching-only copy (guide) or through the addresses.
This recommended if you think the balance is high enough to be concerned with the security.