Also had one die between uses. I picked up a 3450 from the yard that wouldn't take/hold a charge. Thought I might be able to resurrect it with a different charger. So I get home after five months away, hook the ys tekkeon to my other charger and it still won't take a charge. So I check a 3450 I've used for a couple years. No lights. Hook it to a charger. Light turns green after a couple minutes. Remove from charger and check level. No lights. Same result with a different charger. So now I have a couple of dead 3450s. Think I'll retire the third as prevention from having it fail in the field. Back to my old standby DVD batts for secondaries and the BatteryGeeks unit for my main recorder.
Not sure if I want to try my hand at replacing cells but I think I will take one apart just to see what all is involved in doing so other than kirk's one word of advice - patience.