I have an older Kindle (can't find the model name or "generation" but it states "Kindle 3.4.2' in the settings). I also recently purchased a Kindle Voyage. I have all the purchases from the older Kindle transferred to the Voyage, but have purchased some new ebooks since then, and would like to have them on BOTH Kindles. They are currently only on the Voyage. So, how do I get the new ebooks downloaded to my older Kindle? I would think that if I purchased both devices, I should be able to share ebooks among the two of them - right?
Your older device is a Kindle Keyboard (3rd-generation).
When you purchase a book from a Kindle, it downloads to that Kindle. When you purchase from the Amazon website, it downloads to whichever Kindle is selected in the 'Deliver to' menu just below the Buy button.
The book is also stored in your Amazon account and can be downloaded to any compatible device that's registered to your account. Most Kindle books can be downloaded on up to six devices at the same time.
To download a book to your Kindle Keyboard, connect it to a wireless network and sync (Menu > Sync & check for items). Go to Archived Items, look for the book, and select it.
You can also go to your 'Content and Devices' page on the Amazon website to deliver books to your Kindle.