Are my batteries shot?

[Ricco1]

In the mornings my batteries are never at more than 45-50% charge, regardless of how long I've cruised/ run my engine the day before. This is the case even if I use very little power in the evening. I had cause to leave the boat last night so used no power at all having cruised for 4 hours during the day. On my return I measured the batteries; 12.3 volts, so 60% charged. This makes me think my batteries might be shot. I have a gas fridge.

 

If I watch a lot of t.v. the charge in the morning is only slightly less than if I watch very little. This makes me think that the batteries are holding the charge OK, but perhaps aren't fully charging up. My alternator is fine.

 

Any thoughts?

[bottle]

Tell us exactly how you are measuring the state of charge.

[Ex- Member]

In the mornings my batteries are never at more than 45-50% charge, regardless of how long I've cruised/ run my engine the day before. This is the case even if I use very little power in the evening. I had cause to leave the boat last night so used no power at all having cruised for 4 hours during the day. On my return I measured the batteries; 12.3 volts, so 60% charged. This makes me think my batteries might be shot. I have a gas fridge.

 

If I watch a lot of t.v. the charge in the morning is only slightly less than if I watch very little. This makes me think that the batteries are holding the charge OK, but perhaps aren't fully charging up. My alternator is fine.

 

Any thoughts?

 

I suspect they could possibly do with a full charge at some time and some equalisation. A good charger and a 240v landline might solve the problem.

[Ricco1]

measure the state of charge with a multimeter at the battery terminals.

 

I should have added: My starter motor packed in 3 weeks ago, a helpful fellow boater very kindly let me hook up to his landline a couple of times. It took 3 hours or so to charge my batteries with the landline. I say fully charge, as much as my batteries would allow, as the fan on my charger stopped and 2 bright lights became one dull one. The following morning, only using one 8 watt light, an hour with a 17 watt television, water pump to wash up and make a brew, was down at 50% charge.

[John Williamson 1955]

Measure the voltage at the terminals when they're on charge. Check for voltage drop between the alternator and battery terminals. Check for voltage drop between the battery and the meter you use to check the charge percentage under load with the engine stopped and while you're pulling your normal load. Finally, check the voltage at the alternator while it's running. Finally, if the batteries aren't sealed, buy a hydrometer and check the specific gravity in each cell. Any digital multimeter will be good enough for the voltage checks.

 

Post the numbers here, and someone should be able to tell you where the problem is, if there is one.

Edited December 21, 2013 by John Williamson 1955

[bottle]

To give an indication of SOC with a volt meter then the batteries need to have been 'rested' nothing in. nothing out for at least an hour longer is better but not always possible.

 

Checking the voltage immediately after charging gives a false reading as the battery has 'surface charge'

 

You say the alternator is working but to check, with engine running, be careful of belts and pulleys, check the voltage at the alternator and at the battery terminals these should be the same (within milli-volts). depending on your alternator the voltage should be between 13.8 and 14.4

 

I am with Julynian post #3 and do think that you have probably been under chrging and the batteries are sulphated and may be revived as he suggests or they are dead.

 

 

The following morning, only using one 8 watt light, an hour with a 17 watt television, water pump to wash up and make a brew, was down at 50% charge.

 

The above usage is very low and I would expect the batteries to be at a much higher SOC but only if they had been fully charged before.

 

If the batteries were not fully charged then the above reading 50% SOC (12.2v) may be correct.

 

From 50% SOC to charged could take over 8 hours and even then they would not be fully charged.

 

All is variable depending on charge amperage available and also the charge voltage.

 

Batteries lose their capacity with age and usage, think of it as a bucket when new you can fill it to the top but with age (rusting) it begins to lose the ability to hold to hold so much, it leaks.

 

You put just as much into the bucket but cannot get it back to full.

 

Eventually more is leaking out than you can put in, knackered bucket battery

[smileypete]

Are they sealed batts?

 

If you're an off grid liveaboard the non-sealed 'open' ones may cope better with typical liveaboard (ab)use.

 

Plus you can top them up or stick a hydrometer in them to help diagnose problems.

 

cheers, Pete.

~smpt~