Possible battery problem

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petermills

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This has probably been raised many times before, but here goes:
My engine will only turn over when BOTH batteries are connected via the battery isolator switch. I have thoroughly cleaned the terminals on both batteries and also the earth connection to the engine but to no avail.
Both batteries have been given a long charge and read in excess of 13 volts but when either of them is connected alone the engine fails to turn over.
The starter motor is new so I am wondering of I have been unlucky to have both batteries give up at the same time. The engine is a 33 hp Vetus diesel and the two batteries are rated at 96 ah each (approximately 2.5 years old).
Before I rush out and replace the batteries I'd like to have some advice please????????
 
Don't presume that the new starter motor is working correctly . I have just replaced a perfectly good battery on a van because the "new" starter motor was faulty . Have you any means of load testing the batteries separately to see if the voltage drops of .
 
petermills said:
This has probably been raised many times before, but here goes:
My engine will only turn over when BOTH batteries are connected via the battery isolator switch. I have thoroughly cleaned the terminals on both batteries and also the earth connection to the engine but to no avail.
Both batteries have been given a long charge and read in excess of 13 volts but when either of them is connected alone the engine fails to turn over.
The starter motor is new so I am wondering of I have been unlucky to have both batteries give up at the same time. The engine is a 33 hp Vetus diesel and the two batteries are rated at 96 ah each (approximately 2.5 years old).
Before I rush out and replace the batteries I'd like to have some advice please????????
Click to expand...

Two points to check:
1) After charging the batteries, leave them for 24 hrs and measure the voltage of each separately. Look for somewhere around 12.7 volts. If a battery is around 11v it's ikely one of the cells is dead.
2) When you press the start button, can you hear the starter motor solenoid clicking in?
 
Piers said:
Two points to check:
1) After charging the batteries, leave them for 24 hrs and measure the voltage of each separately. Look for somewhere around 12.7 volts. If a battery is around 11v it's ikely one of the cells is dead.
2) When you press the start button, can you hear the starter motor solenoid clicking in?
Click to expand...

Agreed.

For a precise assessment of batteries' status separate them first, then charge and check. If using an intelligent charger the charge process may differ between the two optimizing them individually and probably indicating the weaker of them.

After sitting for 24 h and measuring voltage a load test can be done with one of these testers, £15 off eBay.
http://www.ebay.co.uk/itm/Battery-Load-Drop-And-Charging-System-Tester-Test-6V-12V-Batteries-For-Cars-Vans-/121862371620?hash=item1c5f903924:g:s~kAAOSwzhVWqPg4
 
Spi D said:
Agreed.

For a precise assessment of batteries' status separate them first, then charge and check. If using an intelligent charger the charge process may differ between the two optimizing them individually and probably indicating the weaker of them.

After sitting for 24 h and measuring voltage a load test can be done with one of these testers, £15 off eBay.
http://www.ebay.co.uk/itm/Battery-Load-Drop-And-Charging-System-Tester-Test-6V-12V-Batteries-For-Cars-Vans-/121862371620?hash=item1c5f903924:g:s~kAAOSwzhVWqPg4
Click to expand...

Spi D do you have to turn engine over to test the load with those testers?
 
No - not for load testing.
Can be used on any battery (12v) as the tester puts load on the battery and it's meter shows how voltage drops/keep during the process.

If you want to test starter draw or engine charge, you obviously need to run the engine.

Several on the market, same device under several brands

Demo:
 
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