RE: battery question
The voltages given in the original post by poison are right on for a good 4-cell NiCd pack. Three years is not particularly old for a 700 mAh NiCd pack - such packs often last two or three times that long when charged correctly. However, summerwind is correct, the safe thing to do is to cycle the pack to check capacity, then check the self discharge rate over a week per the directions given on the link to RC Battery Clinic.
With regard to replacing the pack with a 6V pack or a higher capacity pack, that decision depends upon what posion is flying. If he is flying 72 MHz with a 40 sized plane and standard servos then the 4.8 V 700 mAh NiCd pack is a fine choice and is more robust, more economical and arguably safer than both higher capacity packs and 5-cell packs. If he is on 2.4 GHz then he really should be using a 6V pack. If he is flying 2.4 GHz, larger models, more servos or digital servos he might want a higher capacity pack.
Redundant packs with two switch harnesses is an excellent safety measure if one can afford the extra weight.
The notion that larger capacity and higher voltage is always better is an over generalization.