Jorgensen, Kamperis, Bortch, Borg and Rittig (2017) evaluated 52 patients with bedwetting that has happened all of their lives. They had the patient suse transcutaneous electrical nerve stimulation (TENS) for 1 hour twice a day for 10 weeks. TENS has been shown to resolve overactive bladder in 51-78% of children. This is done by neuromodulation. The TENS machine I recommend for daytime incontinence.
Forty-seven of these patients completed treatment and none of them experienced a complete resolution of symptoms. This was a very well designed study that was randomized, double blind with placebo. The majority of the children had difficult to treat bedwetting, but even the children that had not received or failed any previous therapy failed to improve.
My opinion: I would not recommend using a TENS machine to help with bladder capacity or to decrease overnight urine production. I continue to use it with patients that have daytime urinary symptoms such as urinary frequency or incontinence that have either failed medication or have chosen not to use medications.