$50 UL Talk Text Web plan - refill only once a year possible

Dear all,

I do have a question regarding the $50 UL Tal Text Web plan. I bought that plan last year in October, because I was in the USA on a business trip. Now I would like to keep the account, because I know that I will be back in the USA in July and October this year, but I do not want to refill my account before I arrive in the USA.

Is there any kind of a limit after which the account will be closed automatically or will it be inactivated at a certain point?

Thanks for your help