Connect the battery to a 12VDC power supply for say 30 seconds. That will put enough into the battery so the charger can now see there is a battery there. I have done this a few times across many types of batteries with the type of modern chargers that need to see a voltage before they will start their cycle. I am sure some will be aghast at such a suggestion however I didnt die, damage anything etc doing this.
The LiFe batteries are a single shot at going low voltage on a cell and are almost never recoverable in my experience. So not likely to recover the batttery but costs nothing to try.
I just heard on the hamRadio 360 Podcast that West Mountain Radio do a computerised battery analyser that has a “bring back to life” function - something like that may be worth looking at if it’s not too expensive.
usually when back home from using mine and thankfully the radio drops out at 11v.
Put back on charge and set the charger to storage mode and prior to going out again fully charge it.
Does you charger show the current and voltage? If it does you can get a ballpark idea if the values are sensible.
As Matt says, keep a close eye on the cell. If it charges up to a good voltage and the charger stops, then you should arrange to 3/4 discharge the cell at a “nice” rate. Not too much or too fast. Then see if it recharges. If it does then it’s probably OK but watch it when charging for a few more times.
If it doesn’t charge properly or fails to charge after discharging then it’s probably toast. Dispose of it correctly (on eBay of course!) and chalk it up to experience.
Did you normally use this for the FT-817? If so buy a cheap 3 cell LIPO if you charger does LIPOs as well as LifePOs. (The 817 is fine on the lower voltage). I’ve been using internal 2.5aAh LIPOs in my 817 for several years. They last about a year to 18 months before they need replacing I’ve found and certainly nothing like $100 to buy. If you want more capacity an external 5Ah 3S LIPO is also quite cheap and those seem to last me 2 years, one I have is over 5 years old and still fine.