My Nikon D40 loses its data & time in less than one week on a freshly charged battery. It does not lose any of the image on the memory card, so I know it's not the memory card. I thought it's supposed to have an internal battery to keep the settings but even when I leave the camera on the charger/battery adapter, it still loses the date and time. I welcome any suggestions about this.

My Nikon D40 loses its data & time in less than one week on a freshly charged battery. It does not lose any of the image on the memory card, so I know it's not the memory card. I thought it's supposed to have an internal battery to keep the settings but even when I leave the camera on the charger/battery adapter, it still loses the date and time. I welcome any suggestions about this.
The internal battery is the one that powers the part of the camera that stores the date and time. You need to change that battery. Look in your camera manual, there will be instructions on how to locate and change the battery. It is a small battery such as used to power wrist-watches and hearing aids, and it is usually found in a compartment on the side of the main battery chamber.

Thanks, JC. The manual doesn't tell me anything about where the internal battery is and I could not find on looking into the regular battery compartment. I didn't find any diagrams or pictures online that would help and Nikon only says send it in for service. Any suggestions about where the internal battery is located and if it's replaceable?

My Nikon D40 loses its data & time in less than one week on a freshly charged battery. It does not lose any of the image on the memory card, so I know it's not the memory card. I thought it's supposed to have an internal battery to keep the settings but even when I leave the camera on the charger/battery adapter, it still loses the date and time. I welcome any suggestions about this.
Please see page 83 of your user guide, where it says:

The Clock Battery
The camera clock is powered by an independent, rechargeable power source, which is charged as
necessary when the main battery is installed or the camera is powered by an optional EH-5 AC
adapter and EP-5 AC adapter connector ( 103). Three days of charging will power the clock for
about one month. If “Clock not set” is displayed in the monitor, the clock battery is exhausted and the
clock has been reset to a time starting at 2006.01.01.00:00:00. Set the clock to the correct date and
time.

Apparently the battery in your D40 is not a typical replaceable clock battery, but rather an internal, rechargeable battery. It seems you will have to send it in to Nikon for service for them to replace the battery.