Csail
N/A
How do you check to see if a 12v eng. start battery is knackered?
Battery
- Thread starter Csail
- Start date
VicS
Well-Known Member
Best way is to take it to a battery specialist who will test it properly.
But take it home, charge it either with a fancy charger, or with a simple one until the volts have been maintained at 14.4 for at least for a couple of hours.
Check it with a hydrometer if you have one and it is not sealed. All cells should show fully charged and read the same.
Let it stand for 12 hours and check the volts with a digital meter. If good it should read at least 12.7 preferably 12.8 Then monitor it daily for as long as possible. The volts will fall quickly during the fisrt few days but should still be over 12.5 a week or two later, preferably 12.6.
You may still need to get it tested with a high discharge tester as it is a starter battery, or just try it!
But take it home, charge it either with a fancy charger, or with a simple one until the volts have been maintained at 14.4 for at least for a couple of hours.
Check it with a hydrometer if you have one and it is not sealed. All cells should show fully charged and read the same.
Let it stand for 12 hours and check the volts with a digital meter. If good it should read at least 12.7 preferably 12.8 Then monitor it daily for as long as possible. The volts will fall quickly during the fisrt few days but should still be over 12.5 a week or two later, preferably 12.6.
You may still need to get it tested with a high discharge tester as it is a starter battery, or just try it!
Billjratt
Well-Known Member
I've been using a wire coathanger (untwisted) as a high discharge tester. Must have wooden handles and must not touch anything as it gets hot!. If a well-charged battery drops to about or just under 10volts, a cell is gone. You can tell a healthy battery by how long it takes to charge (as well as discharge) If the charge voltage rises quickly it is probably knackered. Just think how long you would want a battery to run (say ) a 4amp fridge - 25 hours? then it would take that long for a 5amp charger to refill it.
tobble
Well-Known Member
Agree with billjrat, the minimum faf method. Alternatively to messing around with coat hanger, hold a volt meter across terminals and tun the engine over (or try to). Seems a little safer to me... the 10V quoted seems to vary, I've heard 9.5 but it's academic really.
There is another test... can you start the engine?! If it's getting unreliable (i.e. complains when cold etc.), then get a new one. it's not rocket. (science)
There is another test... can you start the engine?! If it's getting unreliable (i.e. complains when cold etc.), then get a new one. it's not rocket. (science)
William_H
Well-Known Member
Yes the engine itself is the best discharge tester. If it has become slow to crank the battery is probably knackered.
That is assuming you are sure it has been charged well. Use a voltmeter to check the voltage it charges at with engine running.
Check that the voltage on the actual battery terminals falls when cranking. If it does fall to less than 10 v it is knackered. If it doesn't fall but engine is slow to crank put a positive voltmeter on +ve battery terminal and negative on the starter +ve terminal. You should get very little voltage measured when cranking. ie .5 volt or less. Any more indicates bad wiring switch or solenoid.
You can also check the negative supply with a voltmeter lead on -ve terminal of battery and one on starter case. Again you should get very little drop.
If however your battery is more than 5 years old have a new one.
anyway good luck olewill
That is assuming you are sure it has been charged well. Use a voltmeter to check the voltage it charges at with engine running.
Check that the voltage on the actual battery terminals falls when cranking. If it does fall to less than 10 v it is knackered. If it doesn't fall but engine is slow to crank put a positive voltmeter on +ve battery terminal and negative on the starter +ve terminal. You should get very little voltage measured when cranking. ie .5 volt or less. Any more indicates bad wiring switch or solenoid.
You can also check the negative supply with a voltmeter lead on -ve terminal of battery and one on starter case. Again you should get very little drop.
If however your battery is more than 5 years old have a new one.
anyway good luck olewill
