Battery and shore power issues

[Popski]

Morning to all here.
I recently experienced an odd power issue and wondered if anyone else has had similar. So I keep the boat on shore power all the time both to keep the fridge going and the batteries topped up. The shore power arrangements here in Gozo are we have a transponder on which you add credit. Usually add around €10 every two weeks for electricity and water. We went to the marina and checked the level of credit and we are down to €4 within 5 days (€20 gone in same number of days). Puzzled by this but not too concerned set off on our journey around 30 minutes cruising anchored and set for the day. After around 3 hours noticed that the house battery was down to 10v and any domestic appliance (head) would only just function. Never had this issue before. Sorry to be long winded but I am trying to determine if the amount of credit used from the transponder, the low level of voltage in the battery have some correlation. Batteries are 140ah and are 3 years old. Checked the charge level of the engine battery that’s at a healthy 13.9v. As soon as I start the engine the voltage level on the domestic battery rises and charges at 12.9v 13.2v the main battery is charging at 14.1v. Back to the marina and re establish shore power and main battery changing at 14v domestic battery charging at 12.6v then shut off all ancillary equipment inc autopilot fridge AIS etc now charging at 13.5v. I hope this thread makes some kind of sense and sorry to be a pain.

 

[dpb]

It sounds to me that the house battery has failed and the charger is working overtime to try and charge it....

 

[jrudge]

Agree

You can easily check in the absence of a tester.

Wait until the battery should be charged ( overnight)

Turn off charger. Leave on some load. Fridges and lights say

Leave for an hour.

If the voltage is below 12 volts then the battery’s is done

3 years from a house battery is probably the lower end of average.

 

[Deleted User YDKXO]

3 years from a house battery is probably the lower end of average.

I would say about average for a domestic battery in the Med given the abuse they get

 

[jrudge]

I would say about average for a domestic battery in the Med given the abuse they get

Shhhhhhhh. Mine have lasted 3 years so far and I don't want them to know any different!

 

[Popski]

Hi and thanks for the response. It’s been suggested that I do a load test on the house battery to see if it’s showing signs of deterioration. I have seen a few vids suggesting that it can be done with a multi meter. Am I correct in thinking 12.6 v is a fully charged battery. I’m off to the boat now and will check it out.

 

[Portofino]

Ok another one , after checking out the batts or replacing said bat(s) is this ........
Takes a while for the penny to drop .
Charger !
Unlike a light bulb they decay with time , they don’t just stop/ pack up making diagnoses easy .
So picture the scene ...........
Typical boat house bats and engines two banks of what ever .
Charger - plugged in on the dock like the Op ,s situation of say 40 ah when new .
But it’s decayed now over time to 4 ah max .
If the boats been unused for 3/4 days you don’t notice , if it’s unplugged from shore power often say daily and doing short runs so the fully functional alternator(s) aren’t really compensating them the batts are getting a hammering unknowingly.

Obviously primary Dx here is duff batts but it would nice to know the charger does what it supposed to do , otherwise you are gonna be eating batts .

 

[jrudge]

Hi and thanks for the response. It’s been suggested that I do a load test on the house battery to see if it’s showing signs of deterioration. I have seen a few vids suggesting that it can be done with a multi meter. Am I correct in thinking 12.6 v is a fully charged battery. I’m off to the boat now and will check it out.

I have has a battery pass a drop test and fail a leave on for an hour with load and check the voltage test. This was an expensive bosche tester.

Last time I used a borrowed elecronic tester and it Identified the dead battery ( which was an engine battery so without messing about leaving load on was an issue) in about 2 minutes.

Just turn charger off, leave load on, have beer then test and you will get your answer.

 

[rafiki_]

Hi and thanks for the response. It’s been suggested that I do a load test on the house battery to see if it’s showing signs of deterioration. I have seen a few vids suggesting that it can be done with a multi meter. Am I correct in thinking 12.6 v is a fully charged battery. I’m off to the boat now and will check it out.

I would expect 13.5v for a fully charged battery.

 

[BartW]

I would expect 13.5v for a fully charged battery.

after charging, and no load, some battery's might read 13.5V,
but after a while, or with a minimum load it will drop,
normally a fully charged battery (lead) is somewhere between 12.3...12.7V

for the OP,

if the battery drops quickly below 12V (with or without a small load) its broken,
pls be aware if the battery has been lowered down to 10V she has been punished very hard,
at that voltage she's drained much more than her usefull charge range
if that happened a few times (without you knowing) for shure she is knackered,

be aware that a lead battery can be used max at 50% of her capacity...
At 50% charge, she should still read min 12V (....or 11,8)

a battery monitor is a very usefull instrument for knowing whats going on with the batt's
on a boat its really worth the investment

 

[Rocksteadee]

A battery being charged:
by an alternator, around 14v;
By a charger, 13.5 to 13.8 (this can depend on what type of batteries and if the charger can be switched from open, sealed or AGM batteries)
A battery fully charged, immediately being disconnected from a charger, anywhere from 12.9 to 13.5. This is “surface charge” and is a bit of a false reading. Put a light load, 1amp or so for 10 mins until reading drops and stabilises. This will be around 12.7 (again depending on type of battery) +/- 0.1. 0.2
This 12.7 is fully charged.
50% charge is 11.7
Fully discharged is 10.7

A note on the last 2 above:
12.7 to 11.7, ie 100 to 50% charge is the ideal working range to prolong battery life. Discharging below 11.7, 50% will considerably shorten life, charging cycles.
Below 10.7 will start irreparable damage of battery

All above is a generalisation and can vary with charger makes, battery types, age of batteries and if they have been regularly cycled and or abused