Dead Battery?

[PetiteFleur]

Went to the boat last week on it's mooring to remove the canvas prior to lift out - one battery was completely dead. Removed today and took home to charge. Tried the small Cetrek charger which did not even light up, checked fuses and sockets all OK so dug out the ancient larger 10A charger of many years vintage. Connected up and nothing - left for a couple of hours when it showed about 3amps, good I thought, it;s charging. I then moved the battery to make more srcure on the bench and reconnected the charger - nothing so I shook the battery when the needle shot up to maximum, there was a click and the zeroed, repeated a few seconds later. I turned thye power off.
Is it totally dead? It's exactly three years old, regularly kept on a maintenance charger over winter and gave no problems this summer. Standard 110A Leisure battery with the common Off-Batt 1-Both-Batt 2 switch.

 

[sarabande]

if a battery is really flat it sometimes needs a long low charge to provide a 'foundation' for the main charging routine to take place.

Does your Cetrak have a desulphating routine ?

 

[VicS]

Sounds like an internal fault if your connections to it were good. Dump it!

 

[Stemar]

I think the first question is, Why did it go flat? It's possible it developed a fault, but I can't think of many faults that would make a battery appear dead and make a simple charger do what your big one is doing - I'm no expert, but that sounds like a starightforward discharge to close to 0%. If so, you may get it back, but it'll probably never be the same again. I did it to both my batteries when the alternator diodes died. The starter battery came back and lasted three or four years, but the domestic refused to hold a charge

Unless you know it's because you forgot to turn the power off when you left the boat, I'd be inclined to take a charged battery and connect it in plcae via an ammeter. Most multimeters have a 0-10amp setting, which is where I'd start, just in case. If that's reading zero, try a lower range, working down to milliamps. Over a month, a 1/10amp leak will bring a 100AH battery down. If you find any discharge, track the leak down by disconnecting things until it goes away.

 

[Marsupial]

As Vic says it has an internal fault, it sounds like one of the plates has broken up - it happens from time to time. Persevering with it could cost you more than a new battery. The last ditch effort to save it is to check the SG of each cell if they are all low then maybe it can be charged but if one or more is very low and the rest are "normal" it's scrap.