Sweat Spot On Battery ?

[Biker1]

My battery appears to accumulating a greasy substance. It is colorless and is only alittle bit which is occurring on the top center of the battery.
If you remove the rear cover and look at the back of the battery, you can see what appears to be a greasy secretion. You can wipe most of it away.
The battery is intact so I don't know if this is a leak? or a type of condensation.
Has anyone experienced this and/or know what this is?
I will try a different battery and see if this happens.