save a cell to h5 file in matlab

How can I save a 1x2000 cells with each cell is a 21x512 matrix into a h5 file in matlab ? It saves all the cells as 1x2000 double and all of them are zeros. I want to save the cells in h5 file to use it in python, if there is another way to do it please let me know, appreciate your help.

for i = 1:length(idxtrain)
    x_train{i} = img_array_prec{idxtrain(i)}(:,:,1);
end
%%
for i = 1:length(idxtest)
    x_test{i} = img_array_prec{idxtest(i)}(:,:,1);
end

%%
savefileh5 = 'traintest.h5'
%%
    try
      h5create(savefileh5,'/train/x_train',[size(x_train,1) size(x_train,2)]);
      h5write(savefileh5,'/train/x_train',x_train);
      catch ME
      warning('File already in folder');
    end
%% 
x_train1 = h5read(savefileh5,'/train/x_train');  %it gives double