Battery panic!

[Amari]

Returning to Amari (pontoon , shore power connected to multistage charger) last night after meal ashore, cabin lights appeared dim. Horror, I found voltage on each battery bank 9.4 volts. Main switch was on 'Both'. Each bank has 2 batteries, each ?90/120 a/hrs. Engine batteries 1 year old,flooded, electrolyte levels OK, not hot or bubbling, indicator window black =discharged. Domestic 4 years old,sealed. Indicators black. I immediately turned off fridge, then I realised the 2 trip switches on main breaker panel tripped. Untripped them and charger resumed. Voltage on both banks immediately rose to 13.5. I left things all night and now 10 hours later 3 of 4 battery indicators show green = charged. Voltage with charger humming is 13.9 both banks. Turning off charger (normally on automatic all the time) voltage both banks 13.5 after 5 minutes.
I assume fuses must have tripped some time yesterday without me noticing and fridge drained the batteries.
grateful for thoughts: Does voltage of 9.4 mean permanent damage to batteries? I suppose ideally fridge should switch off if mains power fails, also would have been nice to have audible alarm of power failure rather than relying on eyeball method.
I am a bit clueless about electricity at the best of times, (despite trying to understand forum discussions which often don't agree!) but here in Turkey not always easy to discuss battery types etc, often have to rely/trust experience of yard. Help, SWMBO is coming out with 2 guests tomorrow!

 

[FlyingDutchman]

I would not worry too much about the batteries.
In the past (25 years ago) I had a car that had no warning buzzer if the lights were on and the engine was switched off. So it happened a couple of times that the battery was totally drained. Pushed the car to start, drove around for an hour or so and problem solved. Never did any harm to the battery. Pretty much the same situation. They don't like it, but that's life!

 

[heerenleed]

A complete drain will certainly shorten your batteries life somewhat, but if they keep their charge the way they did before this drain, they are likely to be fine for now. Don't worry, keep an eye on them but this should be a regular procedure. For a liveaboard, never count on batteries to live longer than 3 years (says our battery specialist). If they do, count your blessings.

cheers
Peter

 

[ccscott49]

Wouldnt worry unduly, repeated flattening of batteries will bugger them, but once and it will be ok, theey werent totally flat anyway!

 

[Bilgediver]

Find a battery voltmeter...IE a voltmeter with an expanded analogue scale or a digital meter and mount it somewhere it is easily seen .

Jut did this for brother in law who was always concerned if charger was doing its stuff and now he sleeps at night /forums/images/graemlins/smile.gif

 

[Amari]

Many thanks for this reassurance. I will certainly keep a close watch on the system from now on. I never seem to advance beyond the lower slope of the boating learning curve, at least that's what SHMBO tells me. The taxi driver who took me to Stanstead airport 2 weeks ago asked " Do you have staff? " SWMBO would say ''if only....'' /forums/images/graemlins/laugh.gif

 

[ex-Gladys]

Earlier this year something took our 3*110 AH Squadron AGM domestic bank down badly. They finished up at 4V... Having spent £400 on them last year, I was frantically hoping they would recharge. They did. They don't quite get to full charge, but they are holding 90% easily. I think you will be OK....

 

[boatmike]

If you have proper deep cycle batteries they should not be affected by this. I would however suggest that you fit a voltage sensitive cut out to the fridge circuit to shut it down if the voltage reduces significantly. Most swindleries have such things and they are easy to fit. Also if you have two service batteries dedicate only one to things like the fridge (and eberspacher etc if you have such things) so that if it happens it only drains one battery not both.

 

[skenn_ie]

For liveaboard, and if you have expensive batteries, I would suggest an 'intelligent' charger. They will extend the battery life considerbly, regardless of their use. As far as deep discharge is concerned, most batteries will be degraded if taken below about 80%, with ones intended FOR deep discharge, being able to tollerate about 20%. Actual amount of damage will vary enormously.

 

[Amari]

Many thanks botheras,boatmike and skennie. About to go to bed and hve switched fridge off. I assumed my multistage charger is intelligent. It certainly cost enough ?200GDP. I wonder in retrospect if there was a power cut in the night. Not certain now that fuses had tripped-couldn't remember if 'up' is 'off' or 'on'. You may surmise whatever the intelligence, or otherwise, of the charger that at least it exceeds mine. Very difficult here in Turkey to explain the improvements to electrical circuit you suggest. Thats my excuse, anyway

 

[johnphilip]

Firstly protect the batteries with a FridgeMate, Brilliant item which detects if shorepower or engine is charging and turns on power to fridge.
When no charging power is available it cuts out the fridge but can be overridden with a push button giving 2 hours power to fridge.
http://www.jwmarine.co.uk/

 

[Amari]

Most grateful for this johnphilip. Unfortunate that SHMBO is on the plane at this moment, so too late to bring one out. Will order as soon as I,m on a more secure site (wireless at the mo')
thanks again