To give a concrete example: My company deploys wireless sensor networks. Each sensor periodically reports its battery status, which we store in a database so w

To give a concrete example: My company deploys wireless sensor networks. Each sensor periodically reports its battery status, which we store in a database so we can see which sensors need their battery replaced. Recently we found out that some batteries run empty much quicker than expected. The hardware vendor asked us for 'all battery updates for the past year or so'. We didn't save those; each update was just replacing the current value in the database. So it becomes very hard to diagnose this problem because the historic data is lost.