New Dcb203 Batteries Being Charged With Dcb115 Charger Only Charger To 2 Lights.

We are a public service company that just switched to the 20volt Dewalt battery for use in the 18 volt tools. We got 6 of the conversion kits with the DCB203 battery and DCB115 charger. We alternate 2 batteries between the 18 volt tool and the charger. The tool is used infrequently. Now after just a few months the batteries are starting to only charge to the 2 light level rather than all the way to the 3 lights. We rotate batteries from tool to charger weekly on Fridays and rarely, if ever have the tools been run to the point of running the battery to low charge. This seems to be a fairly common issue with other chargers that will charge without the battery being pushed in all the way, however these chargers are charge or no charge and have no "partial charge" ability/fault. Would this be an issue with a bad lot of batteries/software in the battery or with the chargers?Thank you.