A group of four walkers on Snowdon had to be rescued after being found in the dark - with only a mobile phone torch to light their path.
Ten volunteers from mountain rescue spent three hours dealing with the walkers on Sunday after they failed to leave enough daylight to scale and descend the peak in North Wales.
Llanberis Mountain Rescue Team (LMRT) is asking those walking in Snowdonia to be better prepared.
George Jones, secretary of the LMRT, said: "During the first two days of the New Year there have been four lengthy call outs to attend to inappropriately and ill-prepared groups.
"In one instance on Sunday night, had the group of four carried proper torches rather than depend on a single mobile phone light between them they would not have required the assistance of ten team members for three hours.
"In order to enjoy the mountains in winter it's necessary to prepare for Arctic weather conditions and short days. This is second nature to the experienced walker."
He added the team also dealt with a person who had suffered a "serious arm injury" after slipping on ice on Monday.
He added: "This type of accident might well have been avoided by wearing crampons to traverse the ice."
John Grisdale, LMRT vice chairman, said: "I'd encourage visitors to enjoy the magnificent mountains of Snowdonia in winter but have the wisdom to respect them and to do so safely by preparing carefully."