Thanks for reply, i have done what you told me here is the result below;
1. Before starting - 12.2 V 1 min.
2.-start idling, all electrical off.13.4- 13.8v
Duration 4 min.
All lights, radio , A/C on 13.4 to 13.6 V.
Duration. 2 min.
3.-engine off, 12.7- 12.5 duration 1 min.
1. Should be 12.6 V or more.
2. Should be about 14.3 V.
3. Should be 13+ V, and not drop below 12.6 for weeks.
Could be a bad battery.
Could be a bad alternator, which can cause a battery to go bad.
How old is the battery? Have the terminals ever been cleaned and checked for tightness? Inspect the wire between the alternator and the battery + terminal.
I would give the battery a good charge. See if it takes and holds the charge. If it does, have it load tested.
If the battery checks "good", charge it again, then install it and see how the alternator behaves. The alternator should maintain about 14.3 V.
If the battery checks 'bad", install a new one and see how the alternator behaves. The alternator should maintain about 14.3 V.
If the alternator shows low voltage, have it checked. Don't let it go too long, as it can bring down a good battery.