Just found this article:
Seems lots of people have had the same issue.
Battery is good for about 8 years.
http://www.dailyherald.com/story/?id=388642
By Marni Pyke | Daily Herald Staff
Published: 6/18/2010 12:01 AM
If your I-PASS transponder seems even more quiet than usual, there could be a good reason.
The self-contained batteries in Illinois tollway-issued transponders are likely to expire once they hit the ripe old age of 8 1/2 years.
The Illinois State Toll Highway Authority instituted a pilot program in February reclaiming dead transponders and substituting live ones in the South suburbs.
Thursday, officials made plans to extend the recall effort across the region this summer. About 300,000 transponders will need replacement by the end of 2010.
That number is nothing compared to the 1.2 million transponders that will expire in 2013, which coincides with a buying spree related to a toll increase for cash-paying drivers instituted in 2005.
"We're trying to be proactive in advance of 2013," tollway spokeswoman Joelle McGinnis said.
Starting in July, the agency will be notifying customers with old transponders who will be able to swap them for no cost at Jewel grocery stores or tollway customer service centers, said Mike Catolico, general manager of performance management.
Officials stressed that only people qualifying for the switch-out will receive a letter from the tollway containing a bar code that matches the transponder requiring replacement.
The tollway's replacement pilot project involved 1,751 expired transponders with 74 percent successfully exchanged.
Of the 1,070 returned transponders, nearly all - 1,068 - were dead. New transponders include an expiry date.
Meanwhile, the agency along with fellow members of the E-ZPass consortium are bidding for a new transponder supplier. E-ZPass is a group of 24 toll authorities with electronic collection systems that allows drivers with transponders from agencies in the consortium to use each others' systems.
Options under consideration include a transponder equipped with lights and a beeping sound that indicates if a toll is successfully paid.
Drivers who have not received a letter and are concerned their transponder battery is dead, can check their I-PASS accounts or look at the blue and yellow lights located at toll plazas. If no lights come on, it's a sign the transponder has seen its best days.