Having non-removable batteries is even worse than soldered SSD/RAM, because at least the SSD and RAM are designed to last the lifetime of the product, whereas the lithium-cobalt battery used in mobile phones typically starts to degrade after 500 recharge cycles between 0% to 100% of its capacity. That same battery can last up 3000 recharge cycles if it is only charged and discharged between 20% and 80% of its capacity.
There is a Battery Charge Limit (.apk) app that limits the maximum charge percentage which works with some Android models to extend the battery’s lifespan. However, you have to start doing this when the battery is new for it to really extend the lifespan, and most people won’t think to do this until they start to see battery degradation, when it is generally too late.
I never buy a new phone without doing the following things:
- Check on the XDA Developers forum to see how well that model runs AOSP derivatives. I read the comments at XDA about the AOSP ports for that model to verify that everything works. It is a pain to deal with a phone that only half works. In theory you can keep upgrading the phone’s OS even after the manufacture stops releasing updates for the phone, but it is crap shoot whether this will happen with your particular model. There may not be volunteers to make the ROMs for your model. Android/AOSP releases only support 3 kernel versions, and it may not be possible to upgrade the kernel for your phone, because the drivers released by Qualcomm, MediaTek or Samsung may not work with a more recent kernel. It is generally better to look for phone models which guarantee 2 or 3 years of OS updates (Google Pixel, OnePlus, Galaxy S/Note/Z, Android One models), because it is much easier to do an AOSP port to the next version of Android when using sources from the OEM.
- Check whether the Battery Charge Limit app works on that model–often I can’t find this info online, so it is necessary to try it after buying the phone to find out.
- Lookup the model on the iFixit website to see how hard it will be to change the battery. Sadly, most phones today have glass backs, which makes them liable to crack when trying to open the case. For most recent phones, you need need some kind of heating device (heat gun, heat pillow or blow-dryer), suction cups and a plastic prying device (spudger, guitar pick or credit card).