Battery and charging system load testers.

Load testers can vary from the cheap & cheerful to professional quality units with professional prices to match.
But it should be possible to find a unit like this one on ebay for a reasonably modest outlay:


Bacically you clamp the meter to the battery terminals and check the gauge reading with no load applied, ( you want to be in the 12 - 13V range) then hold the load switch "on" for 10 secs and take a gauge reading.
If the gauge reading drops to much then the battery is suspect. ( you wouldn't want it to go below @ 9V but perferably higher)
If you have low readings put the battery on a charger, then once charged, try again.

Next start the engine, and take a reading with no load applied, (your looking for @ 13.5 - 15V) then hold the load switch "on" for 10 secs and take note of the gauge reading, (you want a reading over 12.25V) again a too great a drop in the reading indicates the charging system is the culprit.

HA dowt if that would have been any use on my battery as it was 90% charged at 1800 hrs and at 0200 hrs it stopped working 100% Would not even power the clock in the car as it had stopped at 0203hrs