New batteries drained

[Kharikola1]

Why is it even though I run my engine for an hour every day using a 75a alternator my two 110a batteries drain by nightfall?

all I run is a water pump and a fridge led and internal  tube lamps! Ta!

Edited August 1, 2025 by Kalapattar

[Rob-M]

Because an hour is nowhere near enough engine running, you want more like three to four hours a day and maybe 8 hours one day a week.

[Crewcut]

Fridges use a lot of power, lights can too depending on type (LEDs use much less). Running your engine for one hour with it's 75 amp alternator will not put 75AH back in to the batteries, depends on their condition and state of charge/discharge but you may, e.g. have half that amount going in running for one hour. There's a battery primer somewhere on here which is very useful to have a read of...

[Arthur Marshall]

An hour a day won't fully charge two batteries. It wouldn't even charge one.

Not sure about the fridge, if that's 12v electric it's no wonder the batteries are flat.

When I lived on, with a minimum set up, gas fridge, lights and  water pump the only real electric drain, with a very tiny 12v TV, I used to get an hour telly watching before that went off and then the lights went out, and I used to run the engine two hours a day. The only way to get them charged enough even for that was a long cruise at the weekend.

It was very frustrating trying to watch Morse, which was a two hour show. I had to get the setup in the first half hour, switch everything off, and then get the denouement in the last half hour if I was lucky. And then go to bed.

 

Edited August 1, 2025 by Arthur Marshall

[Kharikola1]

Hi! Thanks for your reply! The led light is on three way gas fridge and don’t use the 12v option, ta!

2 minutes ago, Arthur Marshall said:

An hour a day won't fully charge two batteries. It wouldn't even charge one.

Not sure about the fridge, if that's 12v electric it's no wonder the batteries are flat.

When I lived on, with a minimum set up, gas fridge, lights and  water pump the only real electric drain, with a very tiny 12v TV, I used to get an hour telly watching before that went off and then the lights went out, and I used to run the engine two hours a day. The only way to get them charged enough even for that was a long cruise at the weekend.

It was very frustrating trying to watch Morse, which was a two hour show. I had to get the setup in the first half hour, switch everything off, and then get the denouement in the last half hour if I was lucky. And then go to bed.

 

I use a gas fridge,

ta!

I have 120w of solar and I’m going to add another 120w in parallel! Hope this is enough?

[Crewcut]

Have a read of the primer which is towards the top of this sub forum...

[MtB]

I'd say your thinking is backwards. The fact that new batteries go flat in a day demonstrates they are not getting enough charging. 

 

More energy is being taken OUT of them than is being put IN. Your task is to find out why this is. 

 

You are at the base of a very steep learning curve but there is plenty of help here available to figure out what is happening. First thing to ask is what (if any) instrumentation do you have installed? And do you understand basic electrical theory (Ohm's Law etc)?

[BoatingLifeUpNorth2]

17 minutes ago, Kalapattar said:

Hi! Thanks for your reply! The led light is on three way gas fridge and don’t use the 12v option, ta!

I use a gas fridge,

ta!

I have 120w of solar and I’m going to add another 120w in parallel! Hope this is enough?

Maybe add some more batteries while you’re at it or maybe once your two new are dead, get a couple of 250 amp ones. You basically haven’t got enough batteries/amps or the means of charging them at present.

Edited August 1, 2025 by BoatingLifeUpNorth2

[Kharikola1]

Ok and thanks for all your replies!

I have an inverter and a unit connected to the alternator which is some battery conditioner?

something like that!

2 minutes ago, BoatingLifeUpNorth2 said:

Maybe add some more batteries while you’re at it or maybe once your two new are dead, get a couple of 250 amp ones. You basically haven’t got enough batteries or the means of charging them at present.

Will more batteries equal even longer charging times though?

5 minutes ago, MtB said:

I'd say your thinking is backwards. The fact that new batteries go flat in a day demonstrates they are not getting enough charging. 

 

More energy is being taken OUT of them than is being put IN. Your task is to find out why this is. 

 

You are at the base of a very steep learning curve but there is plenty of help here available to figure out what is happening. First thing to ask is what (if any) instrumentation do you have installed? And do you understand basic electrical theory (Ohm's Law etc)?

I know nothing about electrics only that my boat runs in 12v and appliances draw in watts. I don’t know what ohms law is!

I have a simple set up and seems batteries aren’t powerful enough to cope! Hopefully solar panels is the way forward!

Edited August 1, 2025 by Kalapattar

[bizzard]

34 minutes ago, Kalapattar said:

Why is it even though I run my engine for an hour every day using a 75a alternator my two 110a batteries drain by nightfall?

all I run is a water pump and a fridge led and internal  tube lamps! Ta!

Electric fridge and flourecent tube lamps use a lot of electric. I expect your charging phones and a laptop too. You would probably need to run the engine for several hours a day. If you have a voltmeter gauge,  with everthing switched off, fully charged is 12.7 volts plus and you should not let that voltage drop below half charged which is roughly 12.2 volts or your batteries won't last long.

[b00ke23]

22 minutes ago, Kalapattar said:

I have 120w of solar and I’m going to add another 120w in parallel! Hope this is enough?

 

I'd say fit as much as you can. I had 480W of solar on my last boat and it was adequate during the summer. Most liveaboards have more solar than this.  

[BoatingLifeUpNorth2]

2 minutes ago, Kalapattar said:

Ok and thanks for all your replies!

I have an inverter and a unit connected to the alternator which is some battery conditioner?

something like that!

Will more batteries equal even longer charging times though?

It will also mean you have more amps and they will last longer between charges. Most boats have at least 4x leisure batteries 500amps ish. You need to do a power usage and work out hot many amps you’re using and take it from there. Are you a livaboard with no shore power?

[Kharikola1]

Thanks for your reply! I use a gas fridge and assume led light wouldn’t consume a lot of power! I charge phone and iPad via an inverter! I plan to change lighting to led, thanks

[bizzard]

3 minutes ago, Kalapattar said:

Thanks for your reply! I use a gas fridge and assume led light wouldn’t consume a lot of power! I charge phone and iPad via an inverter! I plan to change lighting to led, thanks

Inverters don't work for nothing either.

[b00ke23]

I forgot to say, your 120W solar panel will not produce this figure in the UK, only at the equator. As the sun never gets higher than about 60 degrees here the absolute best you'll see is about 80W for a few hours around midday on a clear day in high summer. This is why you need much more solar than you think.

[Kharikola1]

3 minutes ago, BoatingLifeUpNorth2 said:

It will also mean you have more amps and they will last longer between charges. Most boats have at least 4x leisure batteries 500amps ish. You need to do a power usage and work out hot many amps you’re using and take it from there. Are you a livaboard with no shore power?

I am a live aboard with no shore power! I work day shifts but reluctant to run engine past 8 pm

[TheBiscuits]

What make and model of inverter have you got, and do you switch it off when not actively using it?

 

Some inverters, typically older ones, can be the single biggest power usage on a boat system, just by being switched on with nothing plugged in!

 

The other big one is the fridge, but if you are using a gas fridge this isn't the case.  If you were using it in mains 240V mode that would be your biggest power use.

[ditchcrawler]

Have you checked that your alternator is actually working correctly, ie. what voltage are your batteries when its running and what sort of current is going into them.

[Kharikola1]

4 minutes ago, TheBiscuits said:

What make and model of inverter have you got, and do you switch it off when not actively using it?

 

Some inverters, typically older ones, can be the single biggest power usage on a boat system, just by being switched on with nothing plugged in!

 

The other big one is the fridge, but if you are using a gas fridge this isn't the case.  If you were using it in mains 240V mode that would be your biggest power use.

I have a 600w victron inverter and yes I leave it on despite not charging off it sometimes 

I’m running the engine to charge batteries but if I connect a generator will charging times half?

I forgot to add that I also run a macerator and flush on my loo!

It was recommended that I switch off solar charging while running the engine to charge!

Is this correct? Ta!

[MtB]

41 minutes ago, Kalapattar said:

I know nothing about electrics only that my boat runs in 12v and appliances draw in watts. I don’t know what ohms law is!

 

Ok, so Iooking at the bigger picture, I surmise you might be a recently new liveaboard. Might that be correct? 

 

How long did it take for your new set of batteries to begin to display this behaviour? And how long did your old set of batteries last? Answers to these two questions will be helpful as a first step in diagnosing what has gone wrong.

 

 

 

41 minutes ago, Kalapattar said:

I have a simple set up and seems batteries aren’t powerful enough to cope!

 

Here, you demonstrate a common misunderstanding. Batteries only store electricity, they don't create it. You batts are prolly plenty powerful enough but the big picture is you have recently been taking more out of them than you have been putting back in. Can you see that this MUST be the case?

 

(If you have been charging for an hour a day for years with no problems, then suddenly there ARE problems this points to an alternator fault.)

 

 

 

Edited August 1, 2025 by MtB

[magnetman]

36 minutes ago, Kalapattar said:

Thanks for your reply! I use a gas fridge and assume led light wouldn’t consume a lot of power! I charge phone and iPad via an inverter! I plan to change lighting to led, thanks

 

The problem with this statement is that a "gas fridge" also has a setting where it runs on 12 volts. 

 

IF your 'gas fridge' (absorption type not compressor type) is set to run on 12 volts then that is the problem. They use shed loads of power on this setting. 

 

Is your fridge definitely running on gas or might it be switched to the 12v operation. 

 

 

https://www.pirancaravansales.co.uk/caravanning-advice/beginners-guide-to-caravanning/fridges/188-3-way-fridges-dometic-thetford-electrolux

"Fridge Power Type: The most common type of caravan fridge is the three-way absorption fridge. This fridge does not have a compressor and instead have evaporating ammonia as a cooler. The fridge can run on either 12V battery power, 240V electrical hook-up or liquid gas. The controls for selecting how to power the fridge are found on the fridge itself, with switches and a dial or, on newer fridges, a digital display panel."

[Kharikola1]

19 minutes ago, magnetman said:

 

The problem with this statement is that a "gas fridge" also has a setting where it runs on 12 volts. 

 

IF your 'gas fridge' (absorption type not compressor type) is set to run on 12 volts then that is the problem. They use shed loads of power on this setting. 

 

Is your fridge definitely running on gas or might it be switched to the 12v operation. 

 

 

https://www.pirancaravansales.co.uk/caravanning-advice/beginners-guide-to-caravanning/fridges/188-3-way-fridges-dometic-thetford-electrolux

"Fridge Power Type: The most common type of caravan fridge is the three-way absorption fridge. This fridge does not have a compressor and instead have evaporating ammonia as a cooler. The fridge can run on either 12V battery power, 240V electrical hook-up or liquid gas. The controls for selecting how to power the fridge are found on the fridge itself, with switches and a dial or, on newer fridges, a digital display panel."

I’m running old compressor fridge on gas not 12v

I have an ‘Adverc’ unit fitted! Anyone know what it does and is it a hindrance to charging methods? Ta!

[magnetman]

15 minutes ago, Kalapattar said:

I’m running old compressor fridge on gas not 12v

I have an ‘Adverc’ unit fitted! Anyone know what it does and is it a hindrance to charging methods? Ta!

 

It's not a compressor fridge if it is running on gas. It will be an absorption type fridge. 

 

That's why I was interested because on 12v the absorption type use far more energy than the compressor type fridges when they are set to run on battery power. 

 

 

 

 

The basic reason for a 3 way fridge is that when used in road vehicles like caravans they are not allowed to be run on gas while in motion. So it runs on the 12v electric producer by the vehicle alternator and sent to the caravan. 

 

If moored in a campsite with mains electric the owner can select 230V operation as the most cost effective solution. If the caravan is moored at a more basic facility or wild camping then use the gas. 

 

That's what they are for and why they exist. 

 

Most Boats will now have compressor 12v only fridges or mains compressor fridges running on an inverter as they use much less electricity. 

 

 

[Arthur Marshall]

Why charge the phone or laptop by the inverter? That uses a stack of power to convert to 240v, which you don't really need as a car charger will charge both direct from the 12v circuit and, I assume, use much less power. I just connected a standard car cigarette lighter type socket to a 12v plug. It has a USB socket as well. 

I would check the gas fridge. Not sure why there would be an led showing - what make is the fridge? I can't see why an electricity supply would be needed if it runs by gas, mine certainly doesn't .

[Naughty Cal]

1 hour ago, Kalapattar said:

Ok and thanks for all your replies!

I have an inverter and a unit connected to the alternator which is some battery conditioner?

something like that!

Will more batteries equal even longer charging times though?

I know nothing about electrics only that my boat runs in 12v and appliances draw in watts. I don’t know what ohms law is!

I have a simple set up and seems batteries aren’t powerful enough to cope! Hopefully solar panels is the way forward!

No. You are taking more out of them then you are putting back into them.

 

Whatever you take out you have to replace plus some.

 

You are not charging your batteries enough.

30 minutes ago, Kalapattar said:

I’m running old compressor fridge on gas not 12v

I have an ‘Adverc’ unit fitted! Anyone know what it does and is it a hindrance to charging methods? Ta!

Compressor fridges do not run on gas!