Batteries

[hlb]

MF's batteries are three years old. Never caused any probs. always on shore power, trickle charge.. Went to Dinorwick, could not reach the shore power. domestics flat. Used little genny for an hour or two. Domestics went down to 9 V. Looked at batteries, possible loose wire.Tightend. Cruised about 8 knots for two hours? then anchored, Back to 9 V.So flat. Arrived Conarfon, shore power, two days. Arrived Conwy, in the river, no shore power. Morning after still about 12 V in domestic power. After running fridge and stuff. Starting battery showing 12.5 after doing nothing,

Has MF mended her battery problem. She seems to be dropping from 13.5 volts on charge, to about 12.5 off charge. Then the domestics usesing a bit more, cos of fridge and stuff. So about 12 V.

It seems that the problem has come, then gone away by tightening the conection. But taken a few days to do it. Does it take a day or two, to get batteries back to normal.

 

[[2068]]

12.5v or thereabouts off charge is "full". Running things might drag that down to 12v and a bit.

11.5v off charge and no load is "mostly empty".

9v is "completely dead", so it would have taken a while to get anywhere near a full charge back in it, as good chargers slow down to get the last bit in.

 

[Assassin]

Possible explanations:

If there was a loose connection it could drain one battery quicker in the battery pack, this would drop it, and the other batteries voltage from use, if this drop is excessive it may need time to recharge. If excess voltage and current are applied it will do nothing to recharge the battery/battery pack as it needs a very low voltage and current initially to get the battery to accept charge. With the generator or alternator charging them it may be excessive.
Trickling these batteries to a state where they can accept generator or alternator charge would take many hours.

As you put it back onto shore power your charging system if a recent one, would be electronically controlled with a feedback circuit, this would determine the state of the batteries and regulate appropriately. It would sense the discharge and trickle the battery pack with the appropriate current and voltage to a point where it would show a rise to a level where alternator or generator charging would work.

If there is any doubt i would split the battery pack and examine and test individual batteries.

 

[rr_123]

Quite normal for the Starter battery and the domestic to show different charges, your system should be designed to charge the starter battery first and when that's full charge the domestic battery/batteries.

Starter batteries have the ability to deliver a massive whump of power to get the donkeys running, but discharging them too much will knacker 'em, and generally speaking at sea the ability to start the engine is (usually) more important than running the fridge (c:

It could be that your domestic battery had sulphated in which case the alternator wouldn't be able to charge it, but a good modern charger can vary the charge rate to reverse the process, the other technique for desulphating lead-acid batteries is "charge on top of charge" or, yes, taking a day or two to get back to normal


You should aim to keep the starter battery full at all times, and not discharge the leisure batteries by more than about 40% of their rated capacity

I've just bought a boat with the starter battery showing 12.7V (perfect) and a domestic showing 2V which is not recoverable! currently trying to restore an old leisure battery from the garage.

 

[nedmin]

Interesting post as batteries are on my mind at present! Moored behind another boat at present and yesterday I was asked if I could give the owner a hand.3 of his batteries had boiled acid all over the battery box,fortunately the box was water tight.The 3 batteries were boiling hot.He,d noticed the day before that when he got his toolbox out of the lazeret that it was warm in there,he didnt think much about it as it was a hot day. The next day he went for his toolbox and found it was hot! and then noticed the battery prob.He is a pretty keen man so cant imagine he hasnt been topping them up.Looks like one went "down" and took the other 2(in parallel).As my batteries are not easy to get at I,m thinking of fitting thermal switches to them as they are quite cheap,would cost under £20, and could save a disaster.Never heard of a boat catching fire but suppose its possible.