A lot of cheaper LED lights either direct overdrive or underdrive LEDs to the point of either frying LEDs or being dim for a long time. I typically do not mind slight overdrive perhaps 25-30 ma but when you get to 40 ma you will have problems with parallel wired 5mm LED arrays as most will get 40 or less and a few will have a lower Vf resulting inf 50+ ma drive current which all but perhaps the nichias cannot tolerate for long periods.
I had an 8LED 3AAA light that was direct drive and using nimh was a mistake as it fried half the LEDs slowly one by one, I replaced 3 of them before deciding to put 8 26,000mcd LEDs and a dropping resistor inline and now it runs twice as long and is even brighter.
