This is their 18V 1.5ah Lithium+ battery. Out of curiosity I checked the voltage before charging it recently and it was about 7.3V at 2 bars on the battery indicator. I charged it till the charger indicated fully charged. I checked the voltage days after I removed it from the charger and it was around 8V but showing 4 lights on the battery. I put it in my impact wrench, it ran fine. I rechecked the voltage and it was 20.3V. I let it sit for a few minutes and the voltage read ~8V. Did this multiple times and it did the same thing. My other ONE+ batteries read ~20V after charging with 4 indicator lights. Even one of the 4 ah battery that I used in the sting trimmer read 18V at 2 lights on the battery indicator. None of the other ONE+ batteries ever drop in indicated voltage just sitting. Just curious, anybody have any ideas why this is happening. I tried to contact Ryobi twice and gave up after 2 hours on hold .