http://www.battrx.com/18V-NiCd-Sub-C-Rechargeable-Battery-Repair-Kit-p/18v-nicd-2100-mah-sub182100.htm
Here's a link to some replacement batteries we've recommended to customers in the past. Let me know if you need anything else for it and I'll see what I can do.
Noah Smith
Customer Service Rep.
Lectrosonics Inc.
noahs@lectrosonics.com