If the collar isn't working correctly, please don't start training him on it. Dogtra's are known for their inconsistent stim. Especially the older models.
I have a newer model 2300ncp and can feel it at 18, my dogs level is around 35 when not in a high state of drive. It has the 2 hour recharge feature.
The collar is working,I could see the dogs hair twitch. It was the remote part that got a low battery. The dog just wasn't showing any signs other than the hair twitch that he felt it, so I'm not sure what level he feels it at.
I have never heard that dogtras are inconsistent :/