I was in an area without Wi-Fi and had tabs loaded, but a few of them tried to load again and they disconnected. Not only does this use more battery, but it disables tabs that I have open that I want to use when offline.
toggle off Auto Discardable (last column) for the tabs you want after they are loaded.
(haven't tested it myself)
Website developers usually embed codes in their websites to refresh them periodically to always show users fresh content, some websites like Twitter, Facebook etc use Ajax to display new contents without a full page refresh.
alternatively, you can right-click on any website that you wanna use offline in browser and save as .MHTML (a single file). I've used it a lot and works like a charm.