RE: retirement time
Yes you need a lipo charger,
Spontaneous combustion used to be a problem, With current line of "Balanced" chargers it's not a big issue any more.
But they always have that risk, just not a likely as in the past.
I still charge mine where I can watch them or in an area where if it did go up, nothing else would catch fire,,
If I charge them indoors it's on a ceramic dessert plate (don't tell me wife)