This might be base64, Although it is missing the required padding. base64 encoded string lengths are
n is the original string. Padding is done with one or two equal (
=) marks. Since your string is 110 bytes long, it should end with two padding bytes.
Manually adding the two padding bytes (which are sometimes omitted because they're predictable) results in the following hex:
Does this look right to you?
Because more than half the characters in this binary string are relatively low numbers and uppercase letters are at the bottom of the base64 table, it's reasonable to have an encoded string with many uppercase letters.
This is merely a guess, and must be validated by comparing multiple known input/output pairs or by actually reverse engineering the encoding/decoding function.