If it was a lithium cell and you opened it then the fiery result is more or less inevitable. The plates are very close together and lithium batteries hold a lot of energy which it can release at once.

However the cell in your photo is a nickel metal hydride which can give off hydrogen if over charged. I very much doubt it was exposure to light that caused it to catch fire, it is far more likely that you short circuited the internal plates. High discharge current causes them to heat very rapidly to the point of catching fire.

Exposure to air may have resulted in a pyrophoric reaction but definitely not light.

I'll take Battery-Powered Adult Toys for $200 Alex...

Cos some men still think women couldn't possibly know these things, Glanny.

"Mainly for the ladies...", lmao. The absolute sexism and condescending mansplaining is the funniest thing I have read today.

Haha. Yeah. It’s funny but very typical. What would us little women know about batteries.