Several phone calls (I used the old phone) later I found that the cheapest battery pack was $19 plus tax.
Some observations of the original pack revealed that the pack was the size and voltage of 3 Ni-MH AAA batteries.
I could buy 3 of these locally for less than $1.75 each.
NOTE do not use regular AAA batteries for this as you will produce battery waste and possibly electrically destroy your phone from the higher voltage that a regular battery has or start a fire if you forget and plug it into the recharger...
This procedure should work with most cordless phoned that have a molded battery compartment.
Step 1: Remove and disassemble
You will need to cut the shrink wrap off and harvest the wires.
The wires will need to be either cut off or de-soldered.
I chose the later route and desoldered the wires from the pack, possibly from remembering all the movies telling you not to cut the red wire...