[Yaesu] FT-50 Problems.

[KD7JYK DM09]

I have three FT-50 HT's.

In one rig, the backup battery went dead.  I replaced it with a new one from
the factory, no problems.

In the second rig, the backup battery went dead, replaced it with a new
battery from Yaesu, the new battery went dead in about three days.

Now, my third FT-50 has had it's backup battery go dead.

These radios are all 13 years old, so no surprise, but before I replace
another battery, any ideas what would cause a new one to go dead within
days?

Kurt