Rabbi Eliezer Waldenberg (a contemporary Halachic authority in Israel), in his Tzitz Eliezer (16:29), addresses two interesting questions relevant to the practice that many people have to keep a charity box in their home and from time to time place money in the box. Firstly, he raises the question of whether a person bears responsibility in the event that the box is lost. Must he pay the lost amount to the institution to which he had been donating?
Rabbi Waldenberg rules that the individual does not bear responsibility to replenish the lost funds. When a person is given a charity box to keep in his home, he does not assume responsibility for it. His status with respect to the box is not even that of a "Shomer Chinam" (somebody who guards another person's item without pay), the lowest level watchman, who is responsible to pay only in cases of loss or damage caused by his negligence. In our case, the individual does not assume any responsibility for the charity box, not even at the standard expected of a "Shomer Chinam," and thus he is not required to replenish the lost sum of money should the box be misplaced.
Secondly, Rabbi Waldenberg deals with a case where the institution that gave the person the charity box neglected to come collect the money for an extended period of time. May the individual use the money he had placed in the box for a different charitable cause?
Rabbi Waldenberg writes that a person in this situation must endeavor to contact the institution and have a representative come collect the money from the box. If this is not possible, then he may perform Hatarat Nedarim a formal annulment of his "vow" in the presence of three men, whereby he declares that he wishes to use the donated funds for another charitable cause. This procedure effectively annuls his initial donation of the funds, allowing him to now designate them for a different cause.
Summary: If a person loses a charity box that he had kept in his home, he is not responsible to replenish the lost funds. If the institution that gave him the box does not come to collect the donated money, he must try to contact the institution. If he cannot, then he may perform Hatarat Nedarim to annul his initial donation, and then donate the money to a different charitable cause.
