Quoted from jlbintn:In the four slot pack I used a 5817 diode, in the two slot pack I used a 4007.
Are you sure you're installing the 3 batteries the right way around? You might have one installed backwards which is effectively cancelling two batteries out. Can you post a picture of this 4 slot battery holder?
wayout440 you might want to correct your battery diagrams, you have two positives connected together
1N5817 are commonly used as a battery blocking diode because they have lower voltage drop compared to a 1N4007.