Gigaset A400, display goes dark

I received a Gigaset A400 phone call. The person who gave me the battery discharged and finally a trace electrolyte spill onto the plate at the minus of the battery. After cleaning the plate and inserting new batteries, the screen becomes dark as if it is over-contrasted. This symptom is very common. Please help, does it make sense to repair this phone after a battery leak?
Best regards.