Technical Battery

[Keith1950]

I have a 3 ltr motorhome with a battery issue
The engine is very sluggish the first two times of trying to start from cold , the 3rd time it spins fine and starts the engine.
I have a battery tester which has the shunt coil on it that shows the battery in a good state of charge
I connected a spare battery across the jump start Terminal inside the engine compartment and to a bodywork point , the engine fired straight away so the starter is OK
I also have put a braided lead from engine to bodywork .
I don't want to change the battery for no good reason but it's playing on my mind when we are away ,
There is a solar charging system which keeps both sets of batteries charged
Any ideas would help
Cheers

 

[deejays]

I have a 3 ltr motorhome with a battery issue
The engine is very sluggish the first two times of trying to start from cold , the 3rd time it spins fine and starts the engine.
I have a battery tester which has the shunt coil on it that shows the battery in a good state of charge
I connected a spare battery across the jump start Terminal inside the engine compartment and to a bodywork point , the engine fired straight away so the starter is OK
I also have put a braided lead from engine to bodywork .
I don't want to change the battery for no good reason but it's playing on my mind when we are away ,
There is a solar charging system which keeps both sets of batteries charged
Any ideas would help
Cheers

Check all the heavy current connections both plus and minus - most likely a high resistance contact somewhere in the high current starter circuit.

 

[Communicator]

Hi Keith 1950,

Welcome to the forum.
As suggested by @deejays, it seems that you have a high resistance contact in the starter motor circuit.
Your test with the spare battery does appear to have eliminated the most common problem which is the engine block earth strap.
I suggest careful examination of the actual battery earth connection, the CAL4 fuse, and connections of the heavy cable that connects from the fuse, to the jump start point. The clamp connecting to the battery positive should also be checked. These items were not incuded in the circuit when using your spare battery.

The attached diagram was, I think, originally posted by @Anthony489

 

[Keith1950]

Thanks guys , I have tried all those ( ex electrician) .Cleaned all the connectors and used vasoline on them .
That's why my initial thought was lazy starter motor but using jump battery from cold it went first time .
Cheers keith

 

[deejays]

Thanks guys , I have tried all those ( ex electrician) .Cleaned all the connectors and used vasoline on them .
That's why my initial thought was lazy starter motor but using jump battery from cold it went first time .
Cheers keith

Possibly starter fuse perhaps then?