The model 4000 battery can be field replicable. On the older 10Mhz uses one 2032 battery. The newer 12Mhz uses two 2450 batteries. When replacing the battery you must remove all of the connectors. Next you remove the screws on both the front and back of the drive. This will allow you to slide the two pieces of the 4000 apart. The batteries are clearly visible once the two pieces of the 4000 are separated. Replace then reassemble the 4000.
If a memory error occurs upon the next power up of the model 4000 you must clear the memory error by resetting the 4000. See faq on erasing the 4000 memory.