Sorry to hear of your problem with your second-generation Flir One device. I hate it when cool gadgets break. I know it's been a while since you posted but I'll answer in case you still have it or someone has the same questions.
If the app on your phone isn't detecting it after replacing the battery then about the only (easy) thing I can suggest is that you verify that the device's connector is seating all the way into the phone's Lightning/USB OTG port. The first and second generation devices had short connectors that don't work well - or at all - when a phone has a protective case on it. If you haven't already, try using the Flir One with your phone removed from its case.
Regarding repurposing the "Lepton" module inside the Flir One: Yes, it's doable assuming the module itself isn't toasted. I was able to remove the module from a second-generation Flir One and use it with a "tCam Mini" device from Dan Julio Designs that I purchased through GroupGets. The tCam Mini is a standalone thermal camera that connects to your wifi network and is accessible through an app on your phone or desktop computer. Note that some GroupGets campaigns include the Lepton, but you might be able to obtain a tCam Mini without a module so you can use yours.
There may be other devices that may support the specific Lepton module in the Gen 2 Flir One, but you should do some research to make sure they're compatible. I actually came across your question while trying to find info on the modules used by the various Flir One devices because I also have a (different) Lepton from a disassembled Gen 1 unit that I'd like to repurpose.
To extract the module from a Gen 2 Flir One, you'll need to pop the back off like you did to get to the battery, and then remove the five little security torx screws inside. If you don't have a security torx of that size, you might be able to wedge a small screwdriver into the 'stars' and manipulate them enough to get the screws out. Once you tilt-and-slide the board out of the Flir One, you'll need to carefully remove the copper shielding foil from the Lepton module and its shutter mechanism, and then gently pry them out of their socket.
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Be aware, by the way, that Lepton modules are supposed to be pretty sensitive to static damage, so take precautions to avoid creating any spare sparks. When seating the module in a new board, make sure it goes in straight and properly oriented (notice the notches in the socket) and avoid pressing directly on the surface of the shutter mechanism.
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Be aware, by the way, that Lepton modules are supposed to be pretty sensitive to static damage, so take precautions to avoid creating any sparks. When seating the module in a new i board, make sure it goes in straight and properly oriented (notice the notches in the socket) and avoid pressing directly on the surface of the shutter mechanism.
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An alternate approach to all this is to sell the DOA on eBay as not working/for parts and use the money to offset the cost of a new device like the tCam Mini.
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An alternate approach to all this is to sell the DOA Flir One on eBay as not working/for parts and use the money to offset the cost of a new device like the tCam Mini with a more recent Lepton module.
Sorry to hear of your problem with your second-generation Flir One device. I hate it when cool gadgets break. I know it's been a while since you posted but I'll answer in case you still have it or someone has the same questions.
If the app on your phone isn't detecting it after replacing the battery then about the only (easy) thing I can suggest is that you verify that the device's connector is seating all the way into the phone's Lightning/USB OTG port. The first and second generation devices had short connectors that don't work well - or at all - when a phone has a protective case on it. If you haven't already, try using the Flir One with your phone removed from its case.
Regarding repurposing the "Lepton" module inside the Flir One: Yes, it's doable assuming the module itself isn't toasted. I was able to remove the module from a second-generation Flir One and use it with a "tCam Mini" device from Dan Julio Designs that I purchased through GroupGets. The tCam Mini is a standalone thermal camera that connects to your wifi network and is accessible through an app on your phone or desktop computer. Note that some GroupGets campaigns include the Lepton, but you might be able to obtain a tCam Mini without a module so you can use yours.
There may be other devices that may support the specific Lepton module in the Gen 2 Flir One, but you should do some research to make sure they're compatible. I actually came across your question while trying to find info on the modules used by the various Flir One devices because I also have a (different) Lepton from a disassembled Gen 1 unit that I'd like to repurpose.
To extract the module from a Gen 2 Flir One, you'll need to pop the back off like you did to get to the battery, and then remove the five little security torx screws inside. If you don't have a security torx of that size, you might be able to wedge a small screwdriver into the 'stars' and manipulate them enough to get the screws out. Once you tilt-and-slide the board out of the Flir One, you'll need to carefully remove the copper shielding foil from the Lepton module and its shutter mechanism, and then gently pry them out of their socket.
Be aware, by the way, that Lepton modules are supposed to be pretty sensitive to static damage, so take precautions to avoid creating any spare sparks. When seating the module in a new board, make sure it goes in straight and properly oriented (notice the notches in the socket) and avoid pressing directly on the surface of the shutter mechanism.
An alternate approach to all this is to sell the DOA on eBay as not working/for parts and use the money to offset the cost of a new device like the tCam Mini.
Good luck!