The only failure I experienced was a failure to buy one sooner......
One of my favourite purchases that just keeps on giving.
Powers my lights for night riding and/or my garmin gps, cell phone and Petzl Tikka 2XP headlight torch for night reading and early camp dismantling, visits to the bathroom etc.
Love the freedom it offers me and I've never once regretted my purchase.
Yet to meet any one who regrets owning one yet.