https://blog.massdrive.com/2012/03/26/renewing-your-license-...
Still, the life span of these cards could be managed for political gain. Perhaps if the majority part in the state house changes, the valid lifetime for only the ID cards could be shortened.
Thank you for asking the question, I had assumed these cards lasted as long as a driver's license and that is not the case. :-)
You make a good point in that these voter ID cards might have a longer expiration then a driver's license. To my knowledge the expiration period of the ID isn't a part of the legislation. In that case we can probably expect to see the length of time vary from state to state. In that case I would suspect that state's with a shorter valid period might be trying to manipulate the number of legal voters.
Your next thought might be along the lines of accepting expired ID for voting purposes. That's an interesting idea but unlikely to be accepted. In Massachusetts, for instance, you can't buy even a six pack of beer if you cannot produce a valid driver's license. Expired licenses are as good as no license at all in that case.