1. One cell or several
Most codes describe a single cell. A 4LR44 is four LR44 cells stacked inside one case, which is why it gives 6 volts instead of 1.5. A 3LR50 is three cells and gives 4.5 volts.
2. The size is in the name too
A 4LR44 is about 13 mm across and 25.2 mm long, so it is bigger than a single LR44. A 3LR50 is about 16.8 mm across and 49.9 mm long.
3. Where stacked cells are used
Older film cameras and some flash units take a single 6-volt 4LR44. Cameras that take two cells side by side take two 3-volt CR2s instead. Vintage radios, some remote controls and older instruments take a 4.5-volt 3LR50.
4. They need their own holder
A 4LR44 is wider than an LR44 and won’t fit an LR44 compartment. If the device asks for a 4LR44, an LR44 or two LR44s side by side isn’t the same thing and may not make contact.
5. The voltage is what matters
A device built for 6 volts won’t work with 1.5-volt cells, and one built for 1.5 volts can be damaged by 6. Check the manual rather than the shape.