I would be very wary of opening these things up. We had a similar tool for the email/VPN system at work & they needed to be sent away when they failed. From what I was led to believe some contain anti-tamper devices so that opening or removing/replacing batteries etc invalidated the "fixed key" used to create the login code. The result being a locked account.

I'd just buy a new key & keep the existing one as a relic, unfortunately.