dying battery?

[kashurst]

noticed today after a run, once the engines stopped, the port (house) battery voltage rapidly dropped to @ 10v
once engines restarted (they use a different pair of batteries) voltage climbs back up within a minute to @ 13.5v so alternators etc seem to be working.

25 miles later, get back to marina, turn of engines and expected to see the port battery voltage start to drop again, but it didn't!
battery charger seems happy enough so left it to its own devices until the morning when it will all have cooled off.
I think the batteries are @3 years old which on past experience is a bit soon for them to die but it can happen.

It could be a poor connection somewhere which I will check out, but does this ring any bells?

 

[VicS]

noticed today after a run, once the engines stopped, the port (house) battery voltage rapidly dropped to @ 10v
once engines restarted (they use a different pair of batteries) voltage climbs back up within a minute to @ 13.5v so alternators etc seem to be working.

25 miles later, get back to marina, turn of engines and expected to see the port battery voltage start to drop again, but it didn't!
battery charger seems happy enough so left it to its own devices until the morning when it will all have cooled off.
I think the batteries are @3 years old which on past experience is a bit soon for them to die but it can happen.

It could be a poor connection somewhere which I will check out, but does this ring any bells?

You need to see the volts rise to 14 at least before you can say the alternator is working.

Get it fully charged on the battery charger ... so that with no load or further charging for 12 hours the o/c volts is about 12.7 then see how well it retains the charge.

You dont say anything about the charger but I am assuming it is an automatic multistage one with adequate output amps for the Ah capacity of the battery to fully charge it from flat overnight.

You do a battery no favours by taking it below 50% of fully charged too many times. 50% is about 12.2 volts when rested.

 

[Momac]

I have seen good voltage on a battery that came off an overnight charge but had negligible energy in reserve . On closer inspection was dead.
I have also known batteries last many years while others show weakness after two years .

10 volts is very concerning and may very well signify the end.

Any battery that shows sign of weakness may put undue strain on alternator and (if applicable) starter motor with costs eventually greater than that of replacing a battery.
I would also suggest if more than one battery are in a bank replace all at the same time and all batteries in the bank must be identical.

Possible source of batteries
https://www.batterymegastore.co.uk/hankook-xv110-x2.html

.

 

[BruceK]

If your house batteries are in the engine room and the engine room temp is reasonably high then battery life is also significantly affected ( in reference to 3 yr/o)

 

[Rocksteadee]

You need to see the volts rise to 14 at least before you can say the alternator is working

The fact that the voltage is going over 12.7 indicates the alternator is working. A flat battery taking full load from an alt will result in a volt drop, as battery charge increases alternator output voltage will increase to its mor normal 14.2

 

[kashurst]

tested batteries today after a night on the charger - Mastervolt jobbie, seems to be working OK, as all other batts seem very happy.
Iffy batteries showed about 13.5 ish when I switched the charger off. switch on the fridge freezer, voltage collapses almost immediately to 10v
tried both batteries individually, same result - so duff batteries.
got the old ones out and bought a new pair. went and had a lie down Are batteries getting heavier or am I getting old?
will have extra wheatabix in the morning so I can fit the new ones.

 

[Rocksteadee]

Immediately a battery comes off charge the volts will read falsely hi, this is called surface charge. A few amps for a couple of mins will dissipate this to give a more accurate open circuit voltage, should read about 12.7 to 12.9. Appt a load of around 10amps current will drop about 0.5 (depending on size of battery)
As you say once fridge is connected voltage drops to 10 v indicates knackered battery

 

[Assassin]

As above.

I would also check all the connections to be sure, even if you dismantle them and clean them.

One tip is to connect them once cleaned and spray them with a can of spray Waxoyl as this is electrically inert and stops them corroding.