@Rene be careful suggesting just get another one with similar specs the chances are the battery pack needs to be waterproof.
It is also a viable to “jump start” Lithium batteries with the correct charger as long as the cells have not dried up causing leakage as you mention. Unlike other batteries lithium have no real memory effect other than digital that can be reset.
All lithium batteries are dangerous in the wrong hands, but treated with care they are not a problem.