a division of Fargo Enterprises, Inc.
P.O. Box 6505
301 County Airport Rd. #105
Vacaville, CA 95696-6505
I found my battery for $1.38. 10 pack for $6.90. Don't know shipping so the 10 bucks they're screwing you on may end up not being that much.
Varta has a web site. Look up the battery and get the dimensions. I'm sure that any Lithium battery of same dimensions and voltage will work.
For Example, I found the following:
It lists all the battery models it replaces.