The iPad Air supports third-party batteries without issues. The question is if the replacement battery is good or not. However, I have to say that the red flash is quite worrisome. This is a symptom we’ll often see with deeper, logic board related issues, specifically the NAND.
So take a step back, double check your work, look for any damage to the flexes, connectors or the surrounding area on the logic board. I would also re-install the original battery (assuming it was good enough to boot the device prior to replacement) to see if you have the same symptoms. If the original battery allows the iPad to boot properly, then consider the replacement battery to be either bad or deeply uncharged (in which case you can let it charge over night). If the original battery no longer boots the device properly, then you probably damaged something during the repair.
Did you use a third-party battery? Apple seems to make our life harder by not supporting third-party replacement parts. I have an iPad Pro 2019 that is now E-waste because the battery wasn’t supported by apple. Did you buy an iFixit battery?
由 Mason Sayrion 完成的
I purchased and installed an iFixit battery on my iPad Air. It rebooted and operated but the battery charger is not recognized and the device will not recharge.
由 Owen Sweeney Jr 完成的