Analyzing 6 years old battery & 16 data set, can we do load test without buying a load tester?

My battery 6 years old (14D) with a small CCA=390A lasted 6 years. I noticed the battery problem last year (when it was a 5-year battery). I monitored the engine's start up for a year. With a set of 16 cars/batteries, I now know the characteristics of an old battery. I can analyze more data if other people contribute their data. How To Load Test A Car Battery Without Buying A Load Tester.