There's no need to use 2 plugs to ignite the propane. There are 2 on the MW54 because, as you know, they hold the CC in relation to the outer case and to have a spare in case you burn out one.

Do an experiment. Put in new plugs and only use one. When that burns out, see if the other one works. You'll be able to determine if it's your battery that's killing the plug or a hostile CC environment.

I'm not familiar with the Enya #3 but try to pick a plug that has a relatively thick element. Also a little tip. Energize your plug and let cool before teasing the elements out. That anneals the element and makes it less susceptible to breakage.