It's all about risk management. You're gonna do what you're gonna do. You're not going to be electrocuted from a battery in a bathtub. Now, A/C on the other hand....
But say your mod gets water in it, AND the protection on your battery fails. Then your battery will vent.
Under the right conditions, yeah, I'd say there's an elevated risk of harm compared to normal conditions.
As a matter of risking life and limb? I would say no.
But, it is always a good idea to use caution when using an electrical device of any kind in humid, damp, or wet areas.
Also, lithium primaries, (non-rechargeable) when in a thermal overrun condition react violently (explosively) to water.
The good news is, that we use rechargeable lithium-ion batteries which contain no lithium metal, only *"lithium ions that are intercalated into graphite, lithium metal oxides, or lithium salts"* and therefore contain no lithium metal, so are safe around water when thermal.
*source*
http://ehs.whoi.edu/ehs/occsafety/LithiumBatterySafetyGuideSG10.pdf Section 8.3.2