Flat boat battery.

[Lazysloth]

Hello quick question, yesterday we got stuck out at sea as the engine wouldn't restart. I managed to get home by swapping the leisure battery with the engine one. Still quite scary tbh and being new to the scene has kinda put me off a little.

I spoke to a machanic who said the alternator belt must not be tight enough so the engine wasn't Charing the battery properly. However before this the boat had been on shore supply and charged for approx 1 month.

I don't understand how a battery which has been charged can only have the power to start the boat once (even if the engine wasn't charging it at all I'd have expected a battery to restart the engine no problem. )

I guess my question is how can I stop this from happening again, is it worth me having a pair of jump leads to connect the 2 batteries to save swapping them should it happen again in future.

Thanks

Thanks

 

[bowler]

How old is the battery? In my experience of batteries, when they go bad they tend to go quick. I have seen bad batteries not hold charge as you describe.

D

 

[DavidJ]

How old is the battery, if more than 5 or 6 years then replace anyway.
I guess you don’t have a battery link switch like most boats so jump leads a good idea. You may only need one since you probably have common earth.
I don’t buy the alternator belt suggestion. Do you have a voltage meter on the boat.

 

[Hurricane]

I don't understand how a battery which has been charged can only have the power to start the boat once (even if the engine wasn't charging it at all I'd have expected a battery to restart the engine no problem. )

Yep - if the battery is old or knackered, it will do just that - hold a low charge for a short period and then when left without being charged, will die completely.
If it is old or its voltage has dropped below 11 volts (for a 12v batter), just get a new one.
It isn't worth mucking around.
I've now come to terms that batteries are very much consumable - ok look after them but when they are passed it, just replace them.
That applies to engine start batteries as well as the house/service batteries.

 

[ChromeDome]

And when you shop for the new battery, go for a start battery or consumption battery type according to the intended use (apparently a start battery this time).

Buy the biggest capacity battery you can fit/afford.

Assume you have a battery separator already since your leisure battery had the juice to start the engine. If not, then such a separator should be high on your list, to keep the start battery isolated from other consuming devices - and of course no consumers connected directly to the starting battery.

 

[Portofino]

As above , but I will add get yourself a £10 multimeter .
Pop down , unplug it fire it up .
But before do this .
1- put the meter on the bat to see if the charger is kicking out anything? How much V it should be , you have to tool now .
2- unplug the shore power ( or turn charger off ) ……see if the batt V drops it should .You are looking for 12.8-13.4 ish here .
Fire it up.
3 - rev it a bit wait a min or two for the Alternator to excite them check the batt V again = should be above 14 V or greater if the alternator is working ie the volts across the batt go up with the motor running , than my point 2 ^ above .
Switched off the batts V should drop back a little to where you where @2 ^ .

4 Turn it off - go to pub have lunch etc return 3- 4 hrs later or next day if went home and record the V now , a certain time with no charger or engine to see if it’s holding anything.If it’s 11 . Something after a 4 hr lunch or 10 , something the next day it’s knackered.


You can get a cross over switch or in the EU they call them “ parallel “.

Its a relay permanently wired in that temporarily connects both banks remotely ….save s all this swopping malarkey at sea .
You can have fixed voltmeters on the dash and a alternator output and indeed charger out put too …..this stuff is std on bigger boats .
But the X over switch is useful on any split ( Sep Dom + engine ) system like yours , because as you just found out they go with no effective warning esp if you fire up with ing say 10 mins of disconnecting the ( charger ) shore power .

 

[ChromeDome]

Plenty of gadgets and battery monitors around, but the multimeter will give you insight at a fraction of the cost.


Youtube also can be a friend when checking alternator and battery with a multimeter, just be aware that cars normally do not have two batteries, dedicated for their purpose (start/domestic).

Please let us know the boat and engine plus electrics setup if looking for more advice.

 

[simonfraser]

connecting a good battery to a dud one is not necesarily going to work
disconnecting the bad one first is a better move
better still is checking the setup with a volt meter

 

[Momac]

I have known starter batteries to fail suddenly on a few occasions over the years , on cars as well as boats.

 

[Hurricane]

Plenty of gadgets and battery monitors around, but the multimeter will give you insight at a fraction of the cost.

Sorry, I can't agree with that statement.
A simple multimeter will only give you the voltage at the time you connect it.
In the OP's case, a simple multi meter would have read a "good" battery state when he left the shore power.

What you need is a dedicated battery checker or a simpler option that I use, is a voltage meter connected to a big load.
You can then check the battery under load.
One like this:-

Disconnect the battery to be tested.
Connect a tester like the one above and flip the switch.
If the battery holds a good voltage (over 10v) for 10 seconds it should be OK.
You will see a bad battery immediately - also, if you can, look into the cells - a bad cell will boil under this test.

 

[ChromeDome]

The battery tester shown actually is a voltmeter and battery load combined. Works well for a swift load check (I have a couple), but I prefer digital multimeters with thinner, longer wires and multiple modes of measuring.

For amp measuring I use a clamp multimeter in situ, to avoid having to dismantle wires.

If using a multimeter on a battery at rest, then charge the battery and note the voltage, let it rest and note the voltage, then load it by some consumers and note the voltage, then start the engine with the multimeter connected to check voltage increase when alternator is charging, you'll get the picture and in more detail.

IMO

 

[Jim@sea]

Hello quick question, yesterday we got stuck out at sea as the engine wouldn't restart. I managed to get home by swapping the leisure battery with the engine one. Still quite scary tbh and being new to the scene has kinda put me off a little.

I spoke to a machanic who said the alternator belt must not be tight enough so the engine wasn't Charing the battery properly. However before this the boat had been on shore supply and charged for approx 1 month.

I don't understand how a battery which has been charged can only have the power to start the boat once (even if the engine wasn't charging it at all I'd have expected a battery to restart the engine no problem. )

I guess my question is how can I stop this from happening again, is it worth me having a pair of jump leads to connect the 2 batteries to save swapping them should it happen again in future.

Thanks

Thanks

Your battery could be goosed. I once bought a battery for a Nissan Patrol (so it was bigger than normal) I was in France and I bought it from a Nissan Dealer. as I wanted a good one. How wrong I was.
Anyway back in the UK after 15 months the battery was flat. I obviously assumed that my car was not charging, although my diagnostic meter said my car was charging. so I assumed that my car had something which was draining the battery as even if I did a 200 mile trip the car would not start, so I took it to an Auto Electrician hwho said the battery was knackered.
And Nissan uk would not do anything as the guarantee was only for 12 months.
I now believe that when they make a battery if the manufacturer knows that it will only have a 12 month guarantee they are not going to make it to the same standard which they would if they were making a battery with a 3 year battery. Like wot VARTA make. You get what you pay for.

 

[dunedin]

Depending on your shore power battery charger (you don’t give details), it is possible that being left on charge for a month could have damaged the battery.
Even with a sophisticated charger, I tend not to leave boat unattended with the shore power charger on. Batteries can overheat and cause serious problems.

 

[Lazysloth]

So I removed both batteries and took them to Halfords. They tested them and said they are both fine. Can I just clarify that when on shore supply this charges your leisure battery, does it also charge your engine battery? My friend seems to think not which would explain maybe where the issue was...

Thanks

 

[KINGFISHER 9]

I have a gadget called a C-Tek FREE which will get a dead flat battery going in 15 minutes. It works! Be sure to get the remote version without the wires so you can use it on the boat - you can also plug it into the mains as well with another wire if you want to leave it on to condition the battery over time. I've only used it without the mains so far .... recommended. £184 in the UK but worth it if you're stuck at anchor with a flat battery!

 

[Hurricane]

The battery tester shown actually is a voltmeter and battery load combined. Works well for a swift load check (I have a couple), but I prefer digital multimeters with thinner, longer wires and multiple modes of measuring.

For amp measuring I use a clamp multimeter in situ, to avoid having to dismantle wires.

If using a multimeter on a battery at rest, then charge the battery and note the voltage, let it rest and note the voltage, then load it by some consumers and note the voltage, then start the engine with the multimeter connected to check voltage increase when alternator is charging, you'll get the picture and in more detail.

IMO

IMHO, that doesn't really tell you anything.
And, yes, that photo that I posted is a voltmeter and a load.
Just what you need to test a battery.
If you don't put a battery under load, you won't know how it will perform when needed.

That said there are specific electronic battery testers that you can buy to test batteries but I don't think a simple multimeter will work as well as a dedicated tester.

 

[Hurricane]

I have a gadget called a C-Tek FREE which will get a dead flat battery going in 15 minutes. It works! Be sure to get the remote version without the wires so you can use it on the boat - you can also plug it into the mains as well with another wire if you want to leave it on to condition the battery over time. I've only used it without the mains so far .... recommended. £184 in the UK but worth it if you're stuck at anchor with a flat battery!

What is the science behind that device then?
I'm familiar with C-Tec chargers - I had one once but it didn't last.

 

[Portofino]

So I removed both batteries and took them to Halfords. They tested them and said they are both fine. Can I just clarify that when on shore supply this charges your leisure battery, does it also charge your engine battery? My friend seems to think not which would explain maybe where the issue was...

Thanks

See my post #6 .
Get a basic voltmeter and put it across both sets , turn on / off charger , start the engine , leave the boat for while etc

They have a split diode when a dom bank and engine bank are connected. This prioritises the engine bank ,from the engines alternator.But think about it it’s hardly done much if it’s fires up within 3 secs, How ever it’s juice gets topped up first .
Then the diode thingy switches to the dom bank .

As far as chargers go ( your Q ^ ) they should , or yours should have at least two outlets .One for each bank .There’s no priority.There’s no need .It takes shore power 240 V AC and reworks to D.C. 14 v …..just needs connecting .

If you follow the instructions in my post #6 with a tenners worth of voltmeter you should find the weak link ……assuming Halfords are correct .

 

[Portofino]

IMHO, that doesn't really tell you anything.
And, yes, that photo that I posted is a voltmeter and a load.
Just what you need to test a battery.
If you don't put a battery under load, you won't know how it will perform when needed.

That said there are specific electronic battery testers that you can buy to test batteries but I don't think a simple multimeter will work as well as a dedicated tester.

A tenners worth of cheapo volt meter from Lidl or similar tells you all you need to know in conjunction with switching stuff on / off and watching for any changes as per my post #6 .
Opens a pathway to the correct diagnosis.