The code below provides a generalized approach to merge maps and if there is a collision because of same key add those values.
allKeys0 = cellfun(@keys, maps, 'UniformOutput', false);
[allKeys, ~, m] = unique([allKeys0{:}]);
allValues0 = cellfun(@values, maps, 'UniformOutput', false);
allValues = cell2mat([allValues0{:}]);
sumValues = arrayfun(@(x) sum(allValues(m==x)), 1:numel(allKeys));
mergedMap = containers.Map(allKeys, sumValues);
Refer the link below for more information on MATLAB map container.