is 12.9v OK?

[Colvic Watson]

Stupidly left the cabin lights on and the isolator switch connected when we left the boat 3 months ago (very hurried exit) and the batteries went flat for about 4 weeks. Put the batteries on charge and then did the same stupid dumbass thing again. Charged the batteries AGAIN and kept them on float charge for about a week. Then I disconnected them and let them stand for the last 2 weeks. Checked the voltage and they read 12.9v. Are they OK? Ran the radar and lots of 12v lights for about 30 minutes and they didn't crash. The bank is 2 leisure batteries (from Halfords) totalling 200amps.

Would a de-sulphator gizmo aid their recovery?

Thanks, Simon

 

[pappaecho]

I would think that they are just fine. Mine are usually at 13.2 volts with a solar panel attached, providing top up. So standing for 14 days they look fine.

 

[VicS]

12.9v is fantastic if they have been standing without charge for more than 24 hours.
One discharge won't wreck a battery but the more times you do it the greater the effect will be and so will be the length of time they are left discharged.

 

[Colvic Watson]

Of course it was with a £5 multi-volt tester from Maplin, but it can't be that much out! (?) Thanks guys, very reassuring,

Simon

 

[bluedragon]

Oh yes it can!! My £5 Maplin Multimeter (green case) reads 0.2V high at 12V. It's now in the "I'll bin it one day" box. Anyway, 12.7V is still good (fully charged). What you don't know is how much capacity is "fully charged". I've just run a capacity check on my service battery by running the VHF for a few days until the battery reached 50% discharge (measured by SG and open circuit voltage some hours after switching-off). Double this figure to get the capacity. My 85Ah battery was indicating about 60-65Ah actual capacity. Not scientifically accurate I know, but good enough. Two years ago I had a battery that showed a healthy 12.7V but fell off the cliff after a few hours of 3A current draw.

 

[VicS]

[ QUOTE ]
£5 multi-volt tester from Maplin

[/ QUOTE ] They do tend to read a bit high as their batteries start to fail, or so we are told.

 

[William_H]

Yes Blue dragon try a new battery before you bin it. If it still reads high open it up and you may find a tiny potentiometer (variable resistor) about 4mm in diameter with a slot for a screw driver. Try adjusting this to hopefully bring the reading down. This should correct for all ranges.
The meters work on a comparison to a known standard voltage. If that standard falls as in flat battery then the meter over reads likewise the standard is oftyen adjustable to a small degree.
Accuracy is not always guaranteed even thought he meter can read out to .001 volt so check with several meters to get the most likely accuracy.

As for the original poster. Yes you can be dismayed at leaving batteries go flat but don't despair. When the batteries are ruined they will not do the job you want it will be obvious they are dead. Don't worry till then.
olewill

 

[simonfraser]

letting them go flat a few times should be ok, mine survived it too
i'd check the capacity by taking out 40 A and see what happens to the voltage
at 80% charge you should still see about 12.6V

 

[bluedragon]

Thanks...I will try a new battery and the idea of the trimming pot.

 

[Niander]

Now then your not going to do it again then??

remember main switch off!...and gas off!
when you leave the boat.....

remember main switch off!...and gas off!
when you leave the boat.....

remember main switch off!...and gas off!
when you leave the boat.....

 

[VicS]

[ QUOTE ]
you may find a tiny potentiometer (variable resistor) about 4mm in diameter with a slot for a screw driver.

[/ QUOTE ] Thanks for that tip. There is indeed such a pot in the Maplin £5 jobbies. Top left hand corner but quite obvious once the back is off. (You have to remove the back to replace the battery) The trouble is you need to have access to a good quality instrument, which has preferably been calibrated, to check it against.

I hope you are right about that being for calibration!

 

[LadyInBed]

12.7v would be good after a longish stand.
The only real way to check is to use a hydrometer on each cell - Specific Gravity of 1265 to 1275 is good.
Also see Battery Tutorial

 

[Birdseye]

The voltage wont tell you much except that the battery is fully charged. The damage will be to the capacity of the batteries if anything. And most lead acid batteries arent designed to be fully discharged. Car ones wont stand it, traction batteries will - where yours are in that spectrum is impossible to say.

 

[William_H]

high Vic just send me a bill if you stuff up a perfectly good multimeter and I will repay in banana dollars. Obviously this move is the one before discarding the meter into the bin.....but I am pretty confident ...I think. I hope olewill

 

[bluedragon]

As mine is in the "bin" anyway, I'll try it! get back to you all later...

 

[bluedragon]

[ QUOTE ]
Yes Blue dragon try a new battery before you bin it. If it still reads high open it up and you may find a tiny potentiometer (variable resistor) about 4mm in diameter with a slot for a screw driver. Try adjusting this to hopefully bring the reading down. This should correct for all ranges.
The meters work on a comparison to a known standard voltage. If that standard falls as in flat battery then the meter over reads likewise the standard is often adjustable to a small degree.
Accuracy is not always guaranteed even thought he meter can read out to .001 volt so check with several meters to get the most likely accuracy.


[/ QUOTE ]

Ah...the wonders of this forum!! My £5 Maplin Multimeter has been rescued from the recycling box. The batteries were OK, but a tiny adjustment of the trimmer pot did the trick. It now agrees with my other meters that a fully charged battery is actually 12.7V, not 13.0V. Well done William... /forums/images/graemlins/cool.gif /forums/images/graemlins/cool.gif /forums/images/graemlins/cool.gif