I received my 18650 (3000mAh) batteries today. When inserted into the cup I get nothing. It may be because there's not enough "tension" (pressure) against the button unit. Gee, I'm not explaining this too well. I tried "stretching the coil thingy. Didn't help much. Is it safe to insert a washer (metal) into the bottom of the cup or will I blow myself up doing that? 