It is reasonable to expect reduced lifetime on refurbished systems for their batteries, fans, and keyboards, cabling, plastic casing, hinges, light sources for display and indication etc. The value of using pre-owned laptops is questionable unless specifically addressing the favourite brand/models, though for technical people it's a good source of savings, tinkering options and overall fun times.
https://en.wikipedia.org/wiki/Lithium-ion_battery#Battery_life All batteries use chemical elements that wear off depending on: - charge/recharge pattern - number of cycles - temperature - usage pattern (drain current/speed/depth of depletion) - storage pattern - general longevity of the chemical system The laptop manufacturer has calculated a typical usage pattern and expiration date. Much can be done to address this, yet not much can be done to escape the physical and chemical processes. In the end, all batteries age and need replacement, always sooner than desired. What may be worth mentioning is that many unnamed sellers online ship unoriginal, unofficial, knock-off, replacements, or merely lower quality items, some of which may have been binned at the factory and/or exported without quality control. Or simply not as good as the original. There are also better than original parts, when the capacity of the battery may be larger in the same casing. It is reasonable to order a battery when you need it, and not years ahead though see above storage affects the performance. As much as official (branded etc) sales chains bring problems with pricing and availability, it may be worth using them for batteries and recycle responsibly. You can get lucky replacing the elements in the battery pack, though not recommended for people without electrical engineering knowledge. The so called original parts are overpriced, so you can invest the same money in several knock-off batteries and not worry much, or use an external battery + inverter, or better direct feed the DC stabilised as in place of the AC charger. If monstrous battery time is required, one can always use more than one battery, internal and/or external (jump-start packs), car adaptor plug + inverter with the stock AC adaptor etc. Use your imagination what you can stick in a tough rucksack, example can be followed by searching online what amateur radio techs do for their field / mobile stations. For general use though, the internal battery is just as good, and depending on your enthusiasm this can get you far. Much of the above is general knowledge, and personal opinion only. Your mileage may vary greatly, and there are a ton of places for bad practices or bad luck. Some batteries though can last 5-6 years of moderate usage quite well. Please add more interesting suggestions or correct blunt edges.
