Are you measuring the glow output with or without a load? It's quite common for them to read way above 1.5 volts without a load. What lead you to check the voltage? Was it buring out plugs, or were you just curious? The only time I've measured the output on mine was when someone else said their voltage was high. The circuit used in most power panels doesn't actually lower the voltage, it pulses the power on an off. This will cause a voltmeter to read higher than 1.5 volts when there is no load.

I use power panels exclusively. I like being able to adjust the output so I get a consistant glow. I've tried the rechargable glow ignitors and personally don't like them. I hand start my plane engines and I get much more consistant starts by using a power panel. I'm sure there will be many who disagree with me citing things like the possibility of the wire getting caught in the prop or the convenience of being able to carry the ignitor to the flight line in case the engine dies on the runway. However, power panels have worked well for me for years. To keep the wire out of the prop, always set your flight box to the side of the plane and then run the wire under the wing and then over the top. This way when you remove the wire, you have to set it behind the wing and well away from the prop.

To adjust the output, set the knob to low and install a plug into the glow connector. Gradually turn up the output until the glow plug wire is orange. Do not set it so high that it's glowing very bright orange, or even worse, white. I've read that if you drive it too high you can damage the coating on the wire.