Are you using a 9 volt or are you using the small round lithiums? I only use the lithiums in my MagnetoSpeed and I've only had to replace them recently after using the first set for a few years. Personally, I keep a small set of lithium batteries in my range bag for whatever electronics I'll be using (range finder, Kestrel, ear pro, MagnetoSpeed, etc) so if I'm at the range and I see I'm running out of juice, I can just throw in a fresh set of batteries.