testing deep cycle batteries

[crossley]

Yes, I've got my battery head on this evening, have been noticing a distinct lack of battery power and the need for more frequent charging for some time now. I'm running 6 alphaline dc31mf deep cycle batteries in 3 pairs on 24v. They came with the boat and are just over 6 years old. Anyway, I took them home and am testing them one at a time, by fully charging them, then discharging them through a known load,8 amps in my case, and noting the voltage and current every half hour. Today's victim only managed 3 hours, down to 10.5V on load of 7.6A. Adding together all the readings I get 268 watt hours,or 22.35 A/hrs. A long way down on the supposed 125 A/hrs capacity. Yes, I know I'm slightly over the c/20 discharge current,which works out at 6.25A.

Is there any easier or quicker way to determine the capacity of These batteries? Tomorrows victim is on trickle charge overnight,ready for testing tomorrow. It's not even loading up the charger as it should,with only a couple of amps on its showing 15v across it.

Not looking promising is it?

[WotEver]

Sounds like they're dead. Not bad after 6 years.

 

Fully charging and then discharging at c/20 whilst monitoring the voltage is indeed the way to check their current capacity.

 

At 6 years life they might well have died from shedding, Sulphation usually shows up much faster than that. So my guess is that they've been treated well with regular full charges.

 

Tony

[Richard10002]

" I'm running 6 alphaline dc31mf deep cycle batteries in 3 pairs on 24v."

 

They dont look like true deep cycle batteries to me... 125Ah but only 23kg doesnt seem close to heavy enough.

 

Having said that, if they've lasted 6 years you've done well, and looked after them well.

[crossley]

The battery box had some acid in it too,so something was leaking.some of the cases were bulging also.

Rather fancy ripping it all out now and making a nice new battery box out of phenolic ply. I like the look of those tall Trojan l16 batteries,they would take up less floor space too. Really need to get some solar panels though before I get expensive new batteries, no shore supply,it's either run the main engine,or the genny and battery charger. Or I could get a hand start engine and a few oil lamps..

[peterboat]

Full tractions are normally 2 volt cells mine weigh over 450 kilos for the six in one bank same for the other

[by'eck]

" I'm running 6 alphaline dc31mf deep cycle batteries in 3 pairs on 24v."

 

They dont look like true deep cycle batteries to me... 125Ah but only 23kg doesnt seem close to heavy enough.

 

Having said that, if they've lasted 6 years you've done well, and looked after them well.

 

Just bought a set of five myself. Wouldn't for a moment suggest they are quality deep cycle batteries given their weight but they appear to offer good value for money and a four year guarantee for what its worth. Very encouraging they have lasted six years.

 

To the OP, yours are certainly showing all the signs of severely diminished capacity so its time for replacement I'm afraid. Be happy they have lasted this long.

 

ETA: The bulging cases and leaking suggest a cell may have gone short circuit in one or more, so they are effectively being seriously overcharged. DO NOT use them further in this state, there may be a risk of explosion!

Edited April 29, 2016 by by'eck

[WotEver]

The battery box had some acid in it too,so something was leaking.some of the cases were bulging also.

As I surmised previously, they've died the death of all well-charged batteries and shed so much plate material that cells are shorting, resulting in overcharging the rest of them, excessive gassing and electrolyte loss.

 

They've done well.

[crossley]

Tested three of the batteries now as described above. Worst was 17%,best 30% of the original capacity.

Ironically the best performer upto now is the one with the bulging ends. Best price upto now for 4off Trojan l16p is £250 each if I collect. Looking at second hand traction cells too.

[crossley]

Just a final note about the outcome of load testing my old set of batteries, they came in at between 17 to 31% of the stated 125 A/hr capacity.

Broke one open today out of curiosity,just to see what was going on inside. it was full of browny red mud. S.g. Was 1.125 on all cells. Plenty of gravy left in it too.

Tried charging it at 12 amps, all that happened was voltage shot up to 17 volts as it fizzed away, the s.g. Stayed the same.

So the final verdict is they've shed the active material, hence the brown mud when I emptied it out.

So why have they died of plate shedding? If they were undercharged they would be sulphated. If they were overcharged they would be down on electrolyte. Must be that the "cycle life" has been reached.

[cuthound]

Every time you charge or discharge a battery it stresses the plates and a little of the active material falls out. That is why battery life is defined in cycles.

 

Edited to make sense.

Edited May 6, 2016 by cuthound

[WotEver]

So why have they died of plate shedding?

Because that's what all lead acid batteries die of if they're not prematurely killed by Sulphation due to low charging.

 

Tony

[DHutch]

Sounds reasonable.

 

Our batteries are now I think 9 years old, fairly boring if decent spec Exide 'leisure' batteries , but it all depends on use. Ours run the fridge for ten weekends a year, during the day, while the engine is running, and a few lights and water pump in the evening, always left charged. I expect the capacity is well down, but they still do all we need.

 

If on an off grid mooring, then have you have alluded, charging fully is hard. Our batteries are lucky as we are basically moving 8 hours a day any day we are on the boat, and we then leave after a fun day sunday late afteroon without spending that night onboard. However where this is not the case, solar is a great way to ensure batteries get charged fully while your away, perhaps with the engine or a generator being used to get the 'bulk charge' in before the solar does the last 80-90% which takes all the time.

 

 

Daniel