I have before 4gb ddr2 sodimm einzubauen 2gb under windows 10 64bit running out. Otherwise it is the dell latitude e6400. Core2duo + working battery and ner 240gb ssd (already upgraded)
According to this series description for the Latitude E6400
https://www.notebookcheck.com/...617.0.html
2 x 2 GB DDR2 - PC 6400 SO - Dimm should not be a problem.
Unfortunately, this test report gives no information on whether 2 x 4 GB apart from Dell specifications for this notebook model series would be possible.
2 slots a 4 GB are normal. So 8 GB.
You can read the exact specifications in the "User Guide", page 22. Here is the short link to the PDF
From my personal experience, I know that it comes with 4GB modules in devices of this class almost always problems.
A single is sometimes still. But with 2x4GB there's always trouble.
If you can buy such at all.
Thank you for your factual supplement in this topic. ☺