DaveP,,, There actually is a way to check the internal resistance of your Battery and people should do this once in a while with there Batts, once that internal resistance rises in your Batt the Batt should be chucked out. Watch this and it will show you how to check the internal resistance= How to test the internal resistance of a battery - YouTube
You can also google " how to check the internal resistance of a Battery " but the video I posted for you also shows the math and test.
Is there any charger that is built with a tester in it, something that tells what the battery is coming off a full charge? If there is I want one