Nothing.
Not to be short, but that is the answer. Your funds will remain available for your use at any time.
If for some reason we need to return funds to you we will refund the payment method on file. Should that process fail, we will do everything in our power to contact you.
We recommend adding enough funds to cover your postage needs for a reasonable amount of time (30 days). Adding to much results in you not having the use of your funds.
We do not pay interest, or charge any fees for you to store money towards your future postage purchase