A preliminary hearing for John Gisler began Wednesday and was expected to conclude Thursday.

But at the start of Thursday’s court session, defense lawyer Brian Martin informed the judge that a battery that operated Gisler’s hearing implant was dead.

“Without his hearing device, he just can’t hear,” Martin said.

Tulsa County Special Judge Allen Klein rescheduled the hearing to resume Tuesday.

On Wednesday, a teenager testified that Gisler — who he indicated was his “Big Brother” for more than 3½ years — had engaged in multiple types of sexual conduct with him.

Gisler was charged in July with lewd molestation, forcible sodomy and second-degree rape. All three counts involved that youth, now 17.

Prosecutors changed the charges last week to three counts of child sexual abuse, alleging that Gisler abused the teenager at Gisler’s Tulsa home between June 26, 2005, and March 1, 2009.

Prosecutor Jake Cain said those amendments to the charges “fit the evidence.”

The change also exposes Gisler, if he is convicted, to tougher punishment than the original counts allowed.

The three sex-abuse counts each allow a possible life prison term. In this case, the maximum sentences for lewd molestation, forcible sodomy and second-degree rape would have been 20, 20 and 15 years, respectively.

Gisler also is charged with possessing child pornography on a computer.

Gisler, 41, was fired this month from his teaching job at Whitney Middle School. A spokesman for Big Brothers Big Sisters of Oklahoma said in July that he was no longer part of that program.