Re: Zapper anomalies

Seem to have problems getting zappers to last the distance!
One stopped working for some reason. I dismantled it and changed the chip with no success. More recently I got: -a Zapper with 2 freq: 30KHz & 2.5Khz which seemed like a great idea. For the first 5 months or so the zapping was really effective. Must have have killed most parasites at that point & maybe that's why it became less effective. So stopped using it for a months and did unfortunately re-infect. Started using it again. It was still innefective.
I decided to measure voltage at the lead ends: it was as low as 4.5 Volts! Is this the reason it seems to have no or little effect? Or do all zappers lose half the original 9 Vlts at point of contact? The Leads are ultra thin with a (mono) mini plug into zapper box) I've found it difficult to find another lead with mini plug. Any suggestions?
Ross