Before opening car avg 12.5 12.6v. When unlocked droops rapidly close to or below 12v. If I try to start car during this time very difficult or fails to start. But if I wait. After about 5 min the voltage starts to climb back up slowly. Once at about 12.2v it’s fine to start. 
I have been taking out fuses to watch for the jump back up. No luck so far. I did confuse tge hell out of car and it eventually refused to start. Removed batt leads and shorted together for 30 min to clear ecu men. Then started fine. 
anyone Come across this issue. 

btw replaced alternator about 6 mths back and starter motor about 3 mths ago. Car has 250k mikes on it. 

Welcome Joseph,

Two things to check before moving on:-

Alternator output.

Battery efficiency.

Halfords stores should be able to test both items for you. Please come back to us with the results before committing to buy. 

The fact that the alternator was renewed 6 months ago,  does not guarantee that it’s now serviceable. There are a lot of poor quality electrical items on sale. 

What were the symptoms which led you to renew the alternator 6 months ago?

Same question re. starter motor 3 months ago -? 
Age and brand of battery and was it coded to the car if replaced during your ownership? 
Regards,

Gareth. 

The battery is clapped out. You should get it properly tested if you want confirmation, but the drop in voltage under the trivial load of the ignition system shows me it is defective.

Alternator : output 14.7 V 140Amp. it does not require coding to the car. the car was being a bit odd, . I put my bluetooth battery monitor from Caravan on the car and the voltage was dropping each day, when engine running it continued to drop. charging seened to stop completly. new alternator in. which was a pain as had toremove bumper to get it out as engine is a V6. anyway safe to say im a expert at taking the front off he car now.

Starter motor : had just driven to friends house 30 min away. stopped in drive way, went to move the car about a min later, made few bad attempts to start then v bad burn smell from front of car. I disconnected batter quickely as worried about fire. When Finally got the starter motor out serious smell of burn. a mechanic friend was there at the time and said it had burned out.

I had no problems with the car until last few weeks. While it is draining, you cant start the car. once you wait until it comes back up to about 12.2 engine starts fine. does ot matter if short trip or long trip. I must not try to start car when its draining.

I did go to batter company mths back, they said battery was fine, they kept it overnight to charge. this was around the time the alternator failed. Ill go back again as perhaps between alternator and starter motor stresses I may have damaged the battery.

Thanks for allowing us to attempt to help you Joseph. 
Starting at your start:- 

Alternator output at 14.7v - is that with the new/current alternator? You don’t clarify. 
No one has yet commented on coding the alternator to the car. 

‘…charging seemed to stop completely’ - don’t understand - please clarify. 

If the battery was tested months ago and deemed to be fine, that does not mean it’s fine now, so back to the advice you asked for - reinforce-  get it checked, and come back with its % efficiency, and it’s cold cranking current under load etc., before moving on to more complex possibilities. 
Brand of battery and coded to car at time of fitting? 

Hi

1.7 is with the new alternator.

when the alternator failed the charge cycle stopped when engine on, it ran down rapidly over a day. barely made it home from the shop.

original battery, AGM I think.  ill get it tested tomorrow. thanks for the advise

I take it your 1.7v is a misprint for 14.7.

If this battery is 12 years old, then we have really wasted our comments. 
Don’t even waste your time in getting it checked - just replace it.

In case it helps, I’ve used Exide (premium) to good effect - available from Tayna and others. Have a look on EBay.

Don't forget to get it coded to the car.

Please let us know how you get on. 

Replaced battery like fir like AGM. All sorted now. 

Glad to read it Joseph. A shame it has taken three months to resolve, but it demonstrates something I have written of repeatedly, which is how difficult it is to convince people that their batteries are defective and that the replacements need to be coded in cars of the last two decades.