Got it!
Ended up NOT building the query and value outside of the SPUpdateMultipleListItems function. Here is my working code;
$(document).ready(function() { fields = init_fields_v2(); // Get value from a date fieldvar dateCompleted = getFieldValue('DateCompleted',true);var dateComp = new Date(dateCompleted);var strLength = dateCompleted.length;if ((strLength) > 6) {var d = dateComp//Generate ISO 8601 date/time formatted stringvar s = ""; s += d.getYear() + "-"; s += d.getMonth() + 1 + "-"; s += d.getDate(); s += "T" + d.getHours() + ":"; s += d.getMinutes() + ":";//Replace the "Z" below with the required//time zone offset (eg "+10:00" - Australian EST) s += d.getSeconds() + "-08:00";//alert(s);var queryStringVals = $().SPServices.SPGetQueryString();var taskID = queryStringVals["ID"]; $().SPServices.SPUpdateMultipleListItems({ listName: "Custom Aging", CAMLQuery: "<Query><Where><Eq><FieldRef Name='bscParentTask' LookupId='TRUE'/><Value Type ='Lookup'>"+ taskID +"</Value></Eq></Where></Query>", valuepairs: [["DateCompleted", s]] }); }else { alert("Shorter than"); } });
The above code works. I also discovered that the ISO date can have time as either 0:0:0 or 00:00:00, didn't seem to make a difference and both worked for me.
Next I plan on modifying the query to only update items which belong to the the parent and don't have a Date value in their Date Completed fields. Thanks again for all the suggestions.