The Turnigy Micro Tach is an inexpensive little tachometer for measuring propeller speed.
Like most other users seem to report, every time I reach for it, it has a flat battery and battery replacement is a chore.
I measured the ‘sleeping’ current of the device, and it is 25µA which gives it about 8000 hours of sleep time on a CR2032 200mAh battery. 8000 hours might seem a lot, but it is less than a year. Combined with a bit of usage, I am lucky to see 6 months battery life.
I have attached a battery holder to the back to hold two AAA alkaline cells, and wired that in to the internal battery terminals. A AAA alkaline cell has about 1000mAh capacity, about five times the capacity of the original battery and should last up to 4.5 years, depending on usage.