Are my batteries dead?

[cmedsailor]

I have two (x100 amp) batteries connected in parallel for services. The batteries are 5 years old. Today i tried running the windlass (lofrans 1000w) and it was making a click but not turning. Voltage dropped suddenly to 10 (it was so far 12.5+) and even though with the shore power charger on everything was working (except the electric windlass; neither was working with the engine on) and voltmeter was showing 13+ as soon as i was shutting the charger off voltage was dropping to 10 and nothing was working even after charging the batteries for a couple of hours (except some led lights). In other words the batteries could hold any charge. Are the batteries dead? Do batteries just die suddenly like this? The windlass is fine because at some point i connected in parallel the two dead (!) services batteries with the engine battery and it was working just fine.
Thanks

 

[dingdongs]

replace both as they're fubar

 

[cmedsailor]

replace both as they're fubar

You bet i will but what really suprised me is that while they were so far ok, out of a sudden both now seem to be completely dead. So, is this how batteries go flat? Without a warning.

 

[Mrnotming]

Well I have to agree, this is how they fail! if you want confirmation you can open the cell tops if possible and you will see the failed cells fizzing whilst under load.Wear protective goggles.Beware of hydrogen accumulations from trying to charge knackered batteries.
Can result in Hydrogen explosion, and has done to OPs boats.One lucky to escape with life.Visit swindlerly.

 

[TQA]

Before buying new check all your connections.

It would be unusual but not unheard of for both to fail at once. More common is for one to fail usually a single cell collapse then this pulls down the other battery.

 

[Spyro]

Sounds like 1 or 2 cells shorted. Can you split the bank? You could try splitting the bank and charge individually. Maybe one is so bad it's pulling the other down. But it sounds like both are knackered.

 

[dingdongs]

these supply good marine batteries with free delivery.i personally chose the ones that have 2 sets of posts so you can add terminals that are for the smaller wiring jobs you may have.e.g. battery chargers etc
http://www.eurocarparts.com/leisure-batteries

 

[William_H]

As said split the batteries and try each one individually. Unusual they would both die at once but as siad one can pull the other down.
Yes a battery can die so quickly. On 2 occasions in different cars I have driven 10 plus miles after a faultless start. Stopped a t a shop only to find battery completely dead on trying to start up. good luck olewill

 

[westernman]

It would be worth trying an equalization charge - i.e. charge at about 15.5 volts for a few hours.

My shore charger offers this option and it vastly improved the performance of my battery bank.

 

[Tomahawk]

I had two by 12v traction batteries in parrallel.. the first one died ... Possibly because itmwas doing most of the work.. who knows..

I have replaced them with two six volt units innsies making 12v...They seem to work bett wnd keep their charge longer...

 

[cmedsailor]

Two further questions please:
1. If I replace now my two dead 100amp batteries with one 200amp do you see any advantages or disadvantages?
2. If I connect in parallel two same batteries (type and make) but one 80amp and the other 100amp do you see any problem? If there's any problem, even minor, I would prefer not to do this.
Just to add, I don't have any fancy smart controller or whatever is called. Just the alternator (or 20amp charger when using shore power) and a splitter to split between services and engine battery (by the way the engine battery is completely isolated unless I connect all via an extra switch I have for emergency).

Edit: Forget the first question. I have just realised that one 200amp battery is 50+ kilos. NO WAY!!

 

[William_H]

Edit: Forget the first question. I have just realised that one 200amp battery is 50+ kilos. NO WAY!!

That is exactly why large capacity batteries come in 6volt only. I would suggest that it might be somewhat better to buy 2 x 12v batteries connected in parallel because when they fail they can be separated so one may remain useable. But that would be of marginal value.
More likely however you will find 12v batteries more common so likely to be cheaper than 6v batteries for same total capacity.
good luck olewill

 

[Richard10002]

Edit: Forget the first question. I have just realised that one 200amp battery is 50+ kilos. NO WAY!!

That is exactly why large capacity batteries come in 6volt only. I would suggest that it might be somewhat better to buy 2 x 12v batteries connected in parallel because when they fail they can be separated so one may remain useable. But that would be of marginal value.
More likely however you will find 12v batteries more common so likely to be cheaper than 6v batteries for same total capacity.
good luck olewill

A couple of Trojan T105 can be had for about £117 each. £234 for 225Ah @ 12V. A decent 110Ah 12V is about £100, so not much difference.