Is that a 2101 you are using as opposed to a 5101?
2101's are pin compatible with 5101's but are a super power hog and will eat batteries fast as you are seeing.
Check and make sure that should not be a 5101 instead. If so, put a 5101 in a you'll be fine. OR remove the batteries, toss the 2101/5101 and put in a NvRAM and be done with it forever.