Water is not a conductor until something is dissolved in it that is ionic, like salt.
The best way to clean the batteries is with anhydrous isopropyl alcohol and then dry. Same thing with charger. Drying the parts with dry compressor air via a blowgun is also a good thing. Not the canned shit since it will produce condensation.
DO NOT DO THIS WHERE THERE IS AN OPEN FLAME. Under a ventilation hood or outside is better, and avoid breathing in the fumes.
The biggest issue with the charger is if the circuit was live - which I will assume - and how conductive the coffee was. If the circuit wasn't damaged and is cleaned properly ( may have to use some soapy water to carefully to clean the rails if is one of the multi-size battery sleds and rinse a few times) the next issue is going to be the display. Some of the displays have pins soldered to the board others use a sandwiched conductive polymer. If you are fearless, those sandwiched displays are usually held in place with screws, which will allow you to get rid of any liquid that intruded from capillary action and also clean the backlight if it has one.
Proceed at your own risk.
The shit people do with rice may work but if it leaves behind a hydroscopic residue, bad stuph will happen. That is why it is best to get rid of it. Basically I have outlined a procedure I use to recover geotech gear that has had a gasket failure. If I can't find anhydrous isopropyl, most drug stores have 90%.
You can see on the pc board where the coffee was conductive and if it passed any current since there will be reside left where the water was cooked off.