"Lightning" in "lightning cable" is spelt "lightning" and not "lightening". Lightening is "to make lighter", and "pocket-lightening" likely refers to him/her no

"Lightning" in "lightning cable" is spelt "lightning" and not "lightening". Lightening is "to make lighter", and "pocket-lightening" likely refers to him/her not liking to spend money on lightning cables or that he/she thinks that they cost more than they are worth.