Originally posted by stevebrot I would suggest this may not be a good idea. Even a dilute salt solution will discharge the battery quickly and a quick discharge may lead to explosion:
Lithium battery - Wikipedia
I can't say whether such would happen, but I don't think it is worth the risk. I would be inclined to call the local waste disposal people and ask them for suggestions.
Steve
Assuming it is an 8.4 volt battery, discharging it to 6 volts or so will take almost all the energy out of it. Dropping it in salty water afterwards will take it down to ~0 energy (A 1k ohm resistor across the terminals will discharge starting at about 70mW, take the capacity in mWh divide by 40 to get a ballpark number of hours to fully discharge the battery to the point where you don't have to worry about it anymore, this WILL kill the battery)
250ohms will work for a 4.2 volt battery, 2.5kohm for 12.6 volts