Failure rates for rechargeable Li-ion batteries are on the order of one in 10 million cells.
http://cen.acs.org/articles/91/i6/Assessing-Safety-Lithium-I...
http://cen.acs.org/articles/91/i6/Assessing-Safety-Lithium-I...
At a rough guess, the number of cells that fail excitingly are probably a fraction of those that fail overall.
Definitely worth fixing if it's not too hard/expensive, but probably not worth spending much time worrying about it.
How many people in an aircraft say ~200. How many aircraft in the air say ~5,000. Now that 10 million is down to 2-3 per however often those 1 in 10 million chance is supposed to stand for.