Nest Gen 2 Battery won't change low lin
I bought a second hand Nest Thermostat and the battery will not charge. The info has a low lin reading of only 8. I know the unit is defective because I bought a brand new one and wired it the same and it works great with a lin reading of 200. Is the defective unit in need of a new battery? Or is it possible there is something wrong with the base?
Here is a link to the ifixit Nest Learning Thermostat 2nd Generation Battery Replacement guide.
This should help you gain access to the battery.
Once it has been disconnected from the pcb you could test it with a DMM (Digital Multimeter -Voltmeter function) to check its' voltage level.
If it has a very low reading and since it is not responding to being charged it may have been depleted beyond recovery and will need to be replaced.
I've read that the battery is/was especially made for Nest, who do not supply replacements.
The original battery information (as viewed in the ifixit guide) is a 284449 3.7V battery. The 284449 indicates 2.8mm depth x 44mm width x 49mm length.
Finding a battery with such a small depth measure of 2.8mm(combined with the other dimensions) as the original has proved difficult. This is the closest one that I could find. You may have better luck. This battery is a 303040 3.7V battery (3.0mm x 30mm x 40 mm) which makes it 0.2 mm too thick. Hopefully there may be a bit of clearance in the case so that you can use this as a replacement."