Confused about batteries

[Ramlin Rose]

Please go gently and explain like I'm 5, cos I'm new to this & have no idea. Also sorry it's a long post but I don't know what is relevant & what's not so am including everything.

 

I'm boat sitting for a friend. He told me long before I moved in that the leisure batteries were starting to fail and not hold charge. I moved in 2 months ago and it has steadily got worse until now they are barely holding any charge. 

 

The battery display panel inside the boat, the owner tells me, gives different readings depending on whether the battery is currently charging or not. So if I look at it when the sun is out it reads over 13v but he says that's the voltage going into the battery from the solar, not the voltage of the battery itself.

 

In the evenings (without running the engine) presumably it's not charging at all. But it always reads at least 12v without load. The problem is as soon as you use any electricity it starts to drop. You can see it ticking down and after a short time using anything it goes below 12.4 which I'm told is bad for it so at that point I turn everything off. 

 

There's only one solar panel currently & it won't be doing much in this weather so I wouldn't expect much charge. But the other night I ran the engine for an hour & had the inverter on (charging up a hoover & laptop) & soon after I stopped the engine the voltage started to drop visibly and I had to turn things off. 

 

A fellow boater had a look at the batteries for me with a multimeter. There are 4 batteries (cells?). At first he tested each one and got 7v. Then he said, "oops I did it wrong, they are wired in pairs".  He tested again, but still got 7v. He told me I need to replace them as they are totally kaput.

 

I'm confused on various counts: 

 

1. How could they measure the same singly as in pairs? 

2. If each one measured 7v singly, doesn't that mean they are doing really well? (Cos shouldn't they be 6v each to make 12 as a pair?) Which is contrary to my experience of how they are behaving.

3. If they measure 7v across each pair, then why am I getting a readout of over 12v (when not under load) on the display? 

 

I'm clearly not understanding something, can anyone shed some light on it? (Which is more than I've got on my boat at the moment 😔)

 

Thank you!

 

 

 

 

Edited January 8 by Ramlin Rose
To add clarity

[nicknorman]

Some batteries are nominally 6v and so you have two in series to make a nominal 12v. When your neighbour measured it and got “7v” I think that is too vague as the devil is in the detail of the numbers after the decimal point!

 

It would be helpful to know (or see, if you can post a photo) what the battery display actually is, this will give us an idea of its likely accuracy.

 

If it is accurate, then 12.4v is OK and no need to turn stuff off at that point. I would say that down to 12.0v is ok and that is with nothing turned on. When you turn stuff on the voltage will dip a bit, but what is relevant is the voltage with nothing turned on. So I think you can use more juice, no need to turn the lights off at 12.4v. In any case, if the batteries are more or less knackered, abusing them slightly can’t be too heinous.

 

Bear in mind that you won’t get much from solar at this time of year, and to charge the batteries properly you need to run the engine for several hours. If they are flat, maybe up to 8 hours to properly charge flat batteries.

Edited January 8 by nicknorman

[Tony Brooks]

2 x 7V batteries wired in pars (series) will give you 14 volts total.

 

7V per battery is either the charging voltage or something known as surface charge, which will go away once a bit of current has been used.

 

When a battery is on charge, the charging voltage is the battery voltage. The battery voltage will drop once taken off charge. To give much idea about the battery charge we need the voltage with NO charging, NO equipment running and at least half an hour after charging has stopped.

 

Batteries voltage will drop quickly as the surface charge is run down. 12.4V is close to 3/4 charged for optimum battery life. You can safely let it drop to around 12.2 to 12.3 volts.

 

You seem to have no idea about how long you need to charge for and assuming that 12.4 is a true rested voltage reading and not charging voltage or surface charge, then you need to run for several hours, possibly 4 to 6.

 

You will only see slight differences between Nick's post and this one. That is because we don't know exactly what the rested battery voltage is.

Edited January 8 by Tony Brooks

[Alan de Enfield]

It is not only the voltage that needs to be measured but also the capacity (how many amphours it can hold) of the battery(s)

 

You can have a 12v battery he size of a finger nail, you can have a 12v battery the size of a bus - the difference is how many Ah they hold.

 

If a battery is not fully recharged it starts to sulphate, which reduces the Ah holding capability, if a battery is not completely recharged every time the battery has a draw on it and it is not fully replaced the capacity is further reduced. It is still a '12 volt battery' but no longer has the capacity (Ah) to power your equipment

 

It is possible to destroy a new battery within a matter of weeks.

 

Once the battery is sulphated it is almost impossible to get the capacity back - new batteries are required 

 

It is suggested that an 'average' user needs to charge the batteries for 4 hours per day (every day) and 8 hours at weekends.

 

 

 

Edited January 8 by Alan de Enfield

[Tony Brooks]

15 minutes ago, Alan de Enfield said:

It is suggested that an 'average' user needs to charge the batteries for 4 hours per day (every day) and 8 hours at weekends.

 

I note that the OP runs an inverter, that makes me suspect those times may be a bit low for winter.

[Ramlin Rose]

Ok. 

 

Currently the engine is also not working (it stopped working the other day) 

This is a separate problem. 

 

So from the replies it sounds like it's impossible to tell what's going on with the batteries at this point as I'm simply not charging them enough. There's nothing I can do to charge them properly currently so it looks like replacing them is pointless at this stage. 

 

If/when the engine problem is fixed I will try running it for 8 hours and see how the battery functions then. 

 

Meanwhile I have a friend who knows about this stuff & I'm going to test the batteries again with multimeter whilst on a video call with him & see if I get the same readings as the other guy did. Cos I still don't understand how they can be 7v singly and also 7v across a pair, and I still don't understand how either of these readings tallies with the reading on the indoor display.

 

From the replies, it looks like I should test the batteries when it's dark, when they are not charging from the solar, in order to make sure I'm not reading the charging voltage? Have I understood that correctly?

 

@Tony Brooks What I'm referring to is the reading on the indoor display. I'm confused about how the indoor display relates to the four batteries. But late in the evening (so definitely not charging) and with nothing turned on it usually reads 12.73. 

 

@nicknorman I will post pics or figures when I do the testing

 

Thanks everyone, it's getting slightly clearer...

 

 

[Alan de Enfield]

10 minutes ago, Tony Brooks said:

 

I note that the OP runs an inverter, that makes me suspect those times may be a bit low for winter.

 

 

Yes you are probably correct..

 

@Ramlin Rose

I think you need to get the engine running and leave it running for at least 8 hours. start at a 'fast tickover' (maybe 1220-1400 rpm) and as time goes by you can slowly reduce the revs.

 

Don't forget that it is prohibited to run the engine between 8pm and 8am.

 

What sort of electrical monitioring gauges / equipment is fitted in the boat - Picture would help.

 

If it is simply a volt meter plugged into a cigarette lighter socket (for eample) that is useless.

 

Depending on how batteries are connected you can get :

 

2x the voltage of one battery, or

2x the Capacity (Ah) of the battery but with the same voltage.

 

 

[Ramlin Rose]

Thanks @Alan de Enfield for the diagram, I will have a look at how they are connected. 

 

I'll send photos of the monitoring thing (what I'm calling the indoor display). 

[Tony Brooks]

11 minutes ago, Ramlin Rose said:

@Tony Brooks What I'm referring to is the reading on the indoor display. I'm confused about how the indoor display relates to the four batteries. But late in the evening (so definitely not charging) and with nothing turned on it usually reads 12.73. 

 

An indoor display usually, but not always, shows the voltage at the DOMESTIC battery terminals. Most boats nowadays have two different battery banks, usually a single 12V battery to start the engine, and a bank of batteries to run the domestic equipment, so you can still start the engine if you flatten the domestic bank. We do not know if our boat is like this, but most are.

 

The voltage that the meter shows will be the battery voltage or the charging voltage, whichever is higher. Normally, it will be the charging voltage that is higher.

 

12.73 V is good news in one respect, but may be bad news in another. As you say late in the evening we can assume that the voltage is the rested voltage and that value is close to fully charged which is good - BUT:

 

Alan talked about battery capacity and how batteries can easily be destroyed.  In your case, the destruction looks as if it may be chemical changes inside the batteries (sulphation), which means that the battery has lost an unknown amount of chemicals that means it can no longer hold as much electricity as it once did. When batteries sulphate they charge up quickly but also discharge quickly, so on the present information I suspect the batteries may be badly sulphated, but it may be that when you start to charge them fully they will still be serviceable.

[Ramlin Rose]

@Tony Brooks yes, it has a separate starter battery, which seems fine. The engine problem is not to do with the battery, I'm told. 

 

So you are saying that the 12.73 means it's as fully charged as it can get, but the problem is the capacity which will have deteriorated due to sulphate. Thanks that's helped clarify it for me. So it's like an old phone battery saying it's fully charged and then running out very quickly. 

 

Well, if it's filling up to capacity with the dribble of solar it's getting, then it looks like the capacity is very low

 

I'm not at all surprised they are sulphated, if that can happen due to insufficient charging. It was the owner who told me to run the engine for an hour to charge. So if that's what he's been doing then from what you all have said, it sounds like that will be the problem.

 

@nicknorman if I understand correctly, I shouldn't worry about the voltage reading when under load, and should only stop using electricity when it gets down to, say, 12.0 resting. But - if it's not a silly question - how do you tell when it's getting low? Would you recommend turning everything off every hour or so and seeing if the resting voltage has dropped? Obviously not as a long term solution but to get an idea of the current state?

 

 

 

 

 

[jim mitchell]

43 minutes ago, Ramlin Rose said:

Currently the engine is also not working (it stopped working the other day) 

Stopped or would not start, providing some details about that problem and the engine involved, with pictures  would enable members to offer advice - which is a necessacery step before  considering the 'real' state of your batteries.

 

1 hour ago, Ramlin Rose said:

He told me long before I moved in that the leisure batteries were starting to fail and not hold charge

 If he knew they were failing how many months ago?   if not properly charged since then it would seem they have finally been destroyed ((

[Ramlin Rose]

9 minutes ago, jim mitchell said:

 

 If he knew they were failing how many months ago?   

About 6 months ago, but he rarely uses the boat, just spends the odd weekend on it

9 minutes ago, jim mitchell said:

Stopped or would not start, providing some details about that problem and the engine involved

The engine problem is unrelated - it's to do with faulty wiring in the control panel I believe, water getting into it or something. 

 

I'm dealing with one thing at a time, I may post about the engine problem in a new thread sometime. The leisure battery thing is enough for my brain right now

Edited January 8 by Ramlin Rose

[jim mitchell]

3 minutes ago, Ramlin Rose said:

About 6 months ago, but he rarely uses the boat, just spends the odd weekend on it

Well odd weekends with just an hours charging and no real attention to them almost certainly means they will be dead, Please read Tony's, Nicks and other posts regarding how batteries  should be treated, and understand it  before you replace them or as they have said you are likely to kill the next set very quickly.

 

I.m not being negative - just well aware that poor understanding and treatment of batteries is an expensive past time but one too often unwittingly undertaken.

[Tony Brooks]

7 minutes ago, Ramlin Rose said:

@Tony Brooks yes, it has a separate starter battery, which seems fine. The engine problem is not to do with the battery, I'm told. 

 

So you are saying that the 12.73 means it's as fully charged as it can get, but the problem is the capacity which will have deteriorated due to sulphate. Thanks that's helped clarify it for me. So it's like an old phone battery saying it's fully charged and then running out very quickly. 

 

Well, if it's filling up to capacity with the dribble of solar it's getting, then it looks like the capacity is very low

 

I'm not at all surprised they are sulphated, if that can happen due to insufficient charging. It was the owner who told me to run the engine for an hour to charge. So if that's what he's been doing then from what you all have said, it sounds like that will be the problem.

 

 

I am trying to keep things simple, but if that 12.73 volts is for the domestic bank then they are well on the way to fully charged - you are unlikely to get a lead acid boat battery fully charged because it would take far, far too long, so we say 12.7 to 12.8 volts (rested and off charge is a fully charged as it is sensible to get.

 

Yes, exactly like an old phone battery, but you gave that reading late in the evening, after you had, presumably, been using electricity, so for that use of electricity the batteries seem serviceable. If you put the inverter on and then use that to power (say) an immersion heater, air fryer, or vacuum cleaner and the voltage drops fast and does not recover enough when you turn them off, then they probably have lost too much capacity, but remember discharging to 12.2 to 12.3 is perfectly acceptable, and 12.0 now and again is unlikely to cause major damage. 12.73 late in the evening suggests they have sufficient capacity for your needs.

 

It is not only running for an hour a day that is unlikely to be long enough, but also not running at 1200 to 1500 rpm, because at idle the alternator will not be providing the maximum charge.

 

 

5 minutes ago, jim mitchell said:

.m not being negative - just well aware that poor understanding and treatment of batteries is an expensive past time but one too often unwittingly undertaken.

 

Take that to mean that ruining lead acid batteries from under charging happens to so many new boaters, there is no need to feel bad about it as long as you learn.

[Ramlin Rose]

1 minute ago, Tony Brooks said:

Yes, exactly like an old phone battery, but you gave that reading late in the evening, after you had, presumably, been using electricity

 

Ah, no, that reading is when I haven't used any. 

 

I get back from work at 7pm and that's what it usually reads. 

 

I've been barely using any electricity anyway - just 12v led lighting. Not even been using that lately. Just wear a head torch lol. I've used the inverter a handful of times in 2 months, to charge my laptop (normally I charge it at work). Gave up on the hoover, didn't seem possible to charge it enough so I use a dustpan & brush.

 

But it's looking like I don't need to be quite so frugal now that I know "don't let it go below X volts" refers to resting voltage not the reading whilst using electricity.

 

Acknowledged re running the engine at 1200-1500 not idling. Also didn't know this 

 

 

[Tony Brooks]

Just now, Ramlin Rose said:

h, no, that reading is when I haven't used any. 

 

One can never be 100% sure when doing diagnosis by internet, but in that case I think they may be well sulphated, but try running the engine for longer.

 

Also, if the important light use old-fashioned filament bulbs, you can get 12V LED bulbs to fit the same holders, they use far less electricity than filament bulbs. https://www.bedazzledledlighting.co.uk/collections/led-bulbs as an example, and they sell the adaptors you might need.

[nicknorman]

1 hour ago, Ramlin Rose said:

 

@nicknorman if I understand correctly, I shouldn't worry about the voltage reading when under load, and should only stop using electricity when it gets down to, say, 12.0 resting. But - if it's not a silly question - how do you tell when it's getting low? Would you recommend turning everything off every hour or so and seeing if the resting voltage has dropped? Obviously not as a long term solution but to get an idea of the current state?

 

The amount the voltage dips depends on size of the load, so you can get an idea by observing the voltage before and after switching on whatever you are switching on. If it is LED lighting only, then it will be very little. So for example if it is 12.7 when you get back to the boat, and you switch stuff on and it drops to 12.5v within a minute or two, you can add that 0.2v to the present reading to get an idea of the no-load reading. I doubt it would drop as much as 0.2v just with led lighting though.

 

But overall I think we know that the batteries are already knackered and discharging below say 12v is not going to cause a catastrophe, it is just going to slightly shorten the life of the battery. But since it sounds like the batteries are already due to be sent to that retirement home in the sky (aka recycling centre), I can’t see that it matters too much.

[Ramlin Rose]

Thanks @nicknorman. I will stop being so frugal! I'm very pleased about this. Medieval enactments are much better as a summer activity.

[Paul C]

To be honest, if all you can do is monitor voltage, you'll only get a very basic sense of what the batteries are like (good/fully charged, knackered, or somewhere in between).

 

If you're getting back from work at 7pm and being its winter, its hardly worth running the engine for an hour. I assume you work 5 days a week?

[Tony Brooks]

5 minutes ago, Paul C said:

f you're getting back from work at 7pm and being its winter, its hardly worth running the engine for an hour. I assume you work 5 days a week?

 

But with the suspected current state of the batteries, It is probably needs-must in winter. An hour is better than nothing.