Farway Digital Angle Measure and Level with Lasers 

I've had mine for a year and I'm sure as you've found out it it won't lose charge when not in use and hold a good charge when in use. These lithium ion batteries should last 5 years of light homeowner use as long as you don't leave it fully discharged for a long period of time. I use mine for all things homeowner plus I sharpen knifes with a fixed angle sharpener 3-4 times per week and put it through it's paces 3-4v hours a day, sometimes longer finding and keeping sharpening degrees consistent.