Battery Help!

[Captain Yoghurtpot]

Morning again.
Have had to take my time on trying to solve this battery/ starting issue and have again had the cab battery on charge.
Went to start again yesterday and first pull, sluggish but fired and ran well.
Switched of after about 5 mins, tried again and really laboured to turn engine over, and could not.
Have checked all Earth straps and fitted a jump lead on the Negative terminal to the Engine block and it has made no difference.
My question is that , can a battery which is showing 12.7v on a multimeter when standing and thus almost fully charged, still not have enough cranking amperage to turn over the engine?
Can a battery be seen to look as if it is ok on the voltage, but the cranking side to start , has started to, or has already, failed?
We have had no previous problems with the starter motor itself, ie sticking, so I am inclined to think that the batteries ability to hold enough charge to deliver the required ‘oomph’as a cranking amperage , is now gone.
All advice gratefully received and I have read and re-read the thread.
Thanks and have a happy Sunday.

 

[poppycamper]

If you think battery have you measured voltage of it when actually trying to start van?.....If voltage collapses while trying to start then recovers immediately after you release ignition key.... then yes gubd battery.

 

[Richard n Ann]

You've bridged the earth strap so sounds to me like the battery has come to the end of it's life.

 

[Jev88]

Yes a battery can show good volts at rest and collapse when load applied. Multimeter on battery and someone else crank engine....

 

[andy63]

Can a battery be seen to look as if it is ok on the voltage, but the cranking side to start , has started to, or has already, failed?

Yes that's possible.. the battery has to be capable of delivering a large current.. if the vehicle starts easily its only actually used very little capacity in terms of amp hours..
A voltage test while cranking would be needed and if it collapses totally the battery is done..
I think a garage would consider a voltage below around 8volts as a dead battery under cranking
If you could get a good battery to jump with it may help rule out anything amis with the starter motor or wiring..
Abdy

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[philmc79]

Same happened to me, and turned out to be the earth clamp to the starter battery so i would double check that, one min it was fine then next time nothing but multimeter saud 12.4V in the battery.

 

[Tombola]

these are handy, fit and forget
Amazon product ASIN B08F9ZN5XW

 

[Captain Yoghurtpot]

Thanks for all the advice and guidance folks.
Will be trying some new tests over the next few days as time permits, and will advise of the outcome.
Thanks all who replied