Batteries. Bulrush

[Antony Perry]

Hi just had 5 110amp batteries fitted and a new 75 amp alternator. When charging batteries full charged at 13.4volts  roughly but my bmi meter is telling me the batteries are only at 62 percent. Have been told many different explanations one is just concentrate on the volts just like a simple answer not very electrically minded thanks. 

[Rob-M]

How do you know the batteries are fully charged...?  Have you recalibrated your battery monitor to your new batteries...?  What was the amps when the bolts were showing 13.4v and was there still a charging source or was this a resting voltage reading...?

[Tony Brooks]

I would suggest they are nowhere near 62% charged it the charging voltage gradually rose to that 13.4V

 

You can not assess state of charge from the charging voltage. Most battery monitors tell lies on the charge % scale  unless the owner fully understands how to set them up and synchronise them. I would suggest some diligent manual study.

 

Assess state of charge from RESTED voltage. That is voltage WITH NO LOAD BEING DRAW and at least an hour or more after charging stops, or after you have drawn a moderate load for a few minutes. Take: 12.7 to 12.8 as fully charged. 12.5 as half charged and 12.2 to 12.3 as stop discharging now and recharge ASAP.

 

You can assume the batteries are as fully charged as practical when the charging current has dropped to 1 to 2% of battery capacity, so in your case  5 to 10 amps. That must be at 14.2 volts plus.

 

If you do not heed this there is every chance you will destroy your new batteries within weeks or a few months.

 

There is no simple way around this however much you may wish there to be, but once you learn how to set your % meter up and regularly recalibrate it you can rely on it for a week or two afterwards.

 

 

PS when the charging voltage hits 14.2 to 14.5 the batteries will be perhaps 70% charged. Charging lead acid batteries takes many, many hours.

Edited March 5, 2023 by Tony Brooks
Change possible in pra.3 to practical

[MtB]

40 minutes ago, Antony Perry said:

Hi just had 5 110amp batteries fitted and a new 75 amp alternator. When charging batteries full charged at 13.4volts 

 

I think we may have a clue here why your old batteries needed replacing. 

 

Batteries are nothing like fully charged when the terminal voltage during charging is down at 13.4V. Of far more importance is the current at that 13.4V. What is it?

 

I'd suggest your batts are fully charged only when the charge voltage has risen to 14.4V or more, and at the same time, the charge current has fallen to about 5 Amps. 

 

 

[nicknorman]

Yes you need to reach a charging voltage of at least 14.4v (14.6 if the batteries are cold) and maintain that until the current has subsided to 10A or preferably less. Which can take 8 hours or so if the batteries are in a low state of charge.

[beerbeerbeerbeerbeer]

3 hours ago, Tony Brooks said:

Assess state of charge from RESTED voltage. That is voltage WITH NO LOAD BEING DRAW and at least an hour or more after charging stops, or after you have drawn a moderate load for a few minutes. Take: 12.7 to 12.8 as fully charged. 12.5 as half charged and 12.2 to 12.3 as stop discharging now and recharge ASAP.

Don’t mean to railroad this thread but I still find this all hard to do/follow. 
 

It’s really difficult to get a Rested voltage living aboard and using appliances. 

and then others too have told me if your batteries will come to rest to 12.8v then they’re already shagged. 
And they ought to be resting at that 13.somethingv

 

[rusty69]

2 minutes ago, Goliath said:

Don’t mean to railroad this thread but I still find this all hard to do/follow. 
 

It’s really difficult to get a Rested voltage living aboard and using appliances. 

and then others too have told me if your batteries will come to rest to 12.8v then they’re already shagged. 
And they ought to be resting at that 13.somethingv

 

You could always get a smartgauge if you have lead acid batteries.

 

12.8 isn't shagged if the batteries are rested, but it doesn't take into account what the actual remaining capacity of a battery is.

[nicknorman]

3 minutes ago, Goliath said:

Don’t mean to railroad this thread but I still find this all hard to do/follow. 
 

It’s really difficult to get a Rested voltage living aboard and using appliances. 

and then others too have told me if your batteries will come to rest to 12.8v then they’re already shagged. 
And they ought to be resting at that 13.somethingv

 

No, fully charged and fully rested (so as to get rid of any surface charge) they should be 12.7 to 12.8v. When you stop charging it takes quite a long time for the surface charge effect to dissipate, before that the voltage will be higher, so the best way is to discharge say 1% of capacity, then leave for 10 mins, then measure the voltage. But really, if you want to know whether your batteries are fully charged, the only way is to apply 14.4v or more and keep that until the current has subsided to 1 or 2% of capacity.

[Tony Brooks]

51 minutes ago, Goliath said:

Don’t mean to railroad this thread but I still find this all hard to do/follow. 
 

It’s really difficult to get a Rested voltage living aboard and using appliances. 

and then others too have told me if your batteries will come to rest to 12.8v then they’re already shagged. 
And they ought to be resting at that 13.somethingv

 

 

Simply wrong, although when LA batteries start to go faulty they can produce a higher than normal voltage - for a very short while. That may be where the 13V comes from. In any case, if you have much electrical equipment running 24/7 the THEORETICAL fully charged voltage of  around 13.2V will very quickly drop to 12.7 to 12.8V

 

If you are having problems then you can do as Rusty suggested and get a Smartguage or any of the Amp hour counting meters AND learn how to set it up and regularly recalibrate it. That would include assessing the battery capacity a couple of times a year and setting such gauges to reflect the new capacity (for others, all LA batteries will gradually sulphate aand lose capacity).

 

I never had much problem measuring the rested voltage. I usually did it as part of the 2 am tramp and just listened to make sure the fridge is not running. It is far more difficult if you just have to keep an inverter on 24/7 or central heating, but both should be able to be turned off for 15 minutes so there is a chance to recover. I found a 12V LED bulb or two made no noticeable difference to the rested voltage. Remember if do have central heating, a fridge, or an inverter running when you stop charging they will have more or less dealt with the surface charge so you can get a rested voltage in a few minutes.

 

As with everything lead acid battery, it is never exact, all figures and inferences are approximate. Different LA battery technologies and acid strength will give different rested voltage to state of charge figures. It is all just a guide. It is probably more important to see how readings alter over time, so you can spot when things seem wrong that is day to day, not hour by hour.

 

 

[Rob-M]

I base ours on the voltage when I get up in the morning, if it is 12.5v or 12.6v after the fridge has been running overnight I'm not worried.

[Tony Brooks]

8 minutes ago, Rob-M said:

I base ours on the voltage when I get up in the morning, if it is 12.5v or 12.6v after the fridge has been running overnight I'm not worried.

 

A nice pragmatic procedure.

[Lily Rose]

Similar but I normally like to see 12.7 at bedtime with the fridge not running and the surface charge gone.

 

I also hope to see 12.5 in the morning but sometimes I'm too late as the solar has woken up before me.

[Rob-M]

7 minutes ago, Tony Brooks said:

 

A nice pragmatic procedure.

The LAs have lasted nearly 9 years so far so seems to be doing ok.

[Tony Brooks]

5 minutes ago, Rob-M said:

The LAs have lasted nearly 9 years so far so seems to be doing ok.

 

All I would say is that this will not prove that you fully recharge, so there is the possibility of accelerated sulphation. However, your 9 years all but proves that you are regularly recharging them adequately.

[GUMPY]

12.58volts, 6 amp load, 93% soc

According to my VA meter and Smartgauge. I expect it to still be above 90% tomorrow morning.

I will run a mains charge tomorrow PM so batteries are near enough full when I leave.

 

[ditchcrawler]

1 hour ago, Rob-M said:

I base ours on the voltage when I get up in the morning, if it is 12.5v or 12.6v after the fridge has been running overnight I'm not worried.

Similar here but 24 volt

[beerbeerbeerbeerbeer]

14 hours ago, nicknorman said:

No, fully charged and fully rested (so as to get rid of any surface charge) they should be 12.7 to 12.8v. When you stop charging it takes quite a long time for the surface charge effect to dissipate, before that the voltage will be higher, so the best way is to discharge say 1% of capacity, then leave for 10 mins, then measure the voltage. But really, if you want to know whether your batteries are fully charged, the only way is to apply 14.4v or more and keep that until the current has subsided to 1 or 2% of capacity.

Ok, 

thanks,

all sounds about right then,

I’ve a battery monitor so I can keep eye on stuff. 
domestics came to rest at 12.8v yesterday afternoon after a few hours with nothing switched on   
and starter holds a good 13.1 at rest. 

Ive been thinking domestics should rest at 13.something. 
But now I know different. 
 

I’ve a good few days travelling ahead so can get the volts up to 14.4 for a good time each day and put some good life into the batteries. 


 

I’ve a couple more simpleton questions but I’ll let the OP get sorted first. 
I’ll ask later. 
 

👍

 

[Tony Brooks]

1 minute ago, Goliath said:

I’ve a good few days travelling ahead so can get the volts up to 14.4 for a good time each day and put some good life into the batteries. 

 

Possibly another misapprehension. All 14.4V compared with 14.4V will do is get the batteries slightly more fully charged a little bit faster. It is not high enough to do much to reverse any sulphation. However, still good to do, and it will do no harm.