Before a cell opens, it reaches a point where it still conducts but runs down much faster than the others.

 

Hi,
He is running a Fan from the 10V of the battery terminals, that indicates a shorted cell, not an open circuit dried out cell.
E

 

Or at least a very weak cell.

 

Or at least a very weak cell.

The TS is powering a 'I connected a 12V 1.4A' Fan

A very weak cell would have an high internal resistance and so would limit the available current.

The battery clearly has a shorted 2V cell, as the battery gives 10V at approx 1.2Amps.

E

 

Good morning y'all. I appreciate all the banter back and forth.

This morning I checked and the charger was holding the battery at 13.6V. It doesn't indicate what the current is so I don't know if it was working to hold that voltage or not. Five minutes ago I disconnected the charger and plugged the fan in. Voltage has fallen to 10.45. Remember, when I started this thread it was because battery voltage had fallen to 9.29V but after a few minutes it was rising and had risen to 10.12V. Right now it's holding at 10.45 / 10.44. Voltage IS dropping slowly.

Agree that an open cell would be like a blown fuse - no current through the battery at all. As for opening the top of the battery, that won't be easy. I've tried that sort of thing before, adding water to cells of other gel batteries without success. I'm dubious as to whether it will work because it hasn't in the past. But I'll continue to charge then run then charge then run and see what comes of it all.

 

hi Tony.
I have a 6V 4A SLA with same problem, runs and charges as though its a 4V SLA, handy for some jobs.

E

 

Counting the time between my last post and now the voltage had dropped to 10.40V (19 minutes). A 40mV drop.

Would a bad cell (not shorted, not open) explain these results?

 

Just added to the load. A 12V brake light. The two filament type, one for driving lights and one for brakes / turn signal. Voltage dripped to 9.99V. Will let this run a bit to see what comes of it all. It MAY just be a bad cell.

 

Volts at 10.06.

OK, I'm agreeable to the idea of a bad cell. Just how would I tell which cell is the bad one? Any suggestions?

 

Just how would I tell which cell is the bad one?

Not without opening the top of the battery.
If you do that, you may be able to measure the voltage of each cell by using a voltmeter probe touching the plates of the cell or between two cells.
Obviously you need to be careful as the gel is very caustic sulfuric acid.

So what would you do, even if you determined which cell is bad?

 

Top came off easier than expected. OK, now - how do I tell which cell is the problem?

 

So what would you do, even if you determined which cell is bad?

Honestly, I don't know. Perhaps adding a little distilled water maybe ? ? ? I'm really flying in the dark without instrumentation (so to speak).

 

Testing with test lead clipped to the negative terminal and probing with a fine wire into each cell, these are the voltages I found. Starting with the upper right cell I measured

Neg to the top right cell: 668mV.
Neg to the top center cell: 2.8V.
Neg to the top left cell: 4.8V
Neg to the bottom left cell:4.95V
Neg to the bottom center cell: 7.1V
Neg to the bottom right cell: 9.3V

These voltages are after running the load but not putting the battery on a charge.

Just a guess here, but it seems the bottom left cell is the problematic cell. Agree? Disagree? Second eyes is always a good thing.

 

33 minutes later and I've added water to every cell. All cells were low. Very low. Overall I must have added about 3 ounces total. At present the battery charger is reporting 13.7V and it's not going up like it was before to where it was going up to 14.4V. This may just yet be a recovery. If so - great! Now; what to do with this battery?

 

hi T,
As these are SLA cells, were there any signs of venting due to say past over charging.?

When topping up what fluid level did you take as a reference.?

If you overfill with gel/water and reseal you may encounter vent blow outs if you have not left enough 'gas' space inside each cell, take care.!

E

 

hi T,
As these are SLA cells, were there any signs of venting due to say past over charging.?

When topping up what fluid level did you take as a reference.?

If you overfill with gel/water and reseal you may encounter vent blow outs if you have not left enough 'gas' space inside each cell, take care.!

E

Overcharging? No. Cells may have dried out from sitting in a hot car over a long period of time. Even though I'd generally charge the unit at least once every four months, they were all pretty dry. There was no fluid level to meter against for fill reference. I filled them to the brim at first, then removed 3/4 inch below the brim, leaving room for outgassing.

The battery has undergone recharging at a much slower pace than was initially reported. This has been a good sign. At present, I'm seven minutes into a run test with the fan. Voltage started at 12.8V (fresh off the charger) and now running for eight minutes now, 12.57V and appears to be holding stable with very minor drops as the test runs. I will run this test for an hour (hopefully) and report the findings.

At 10 minutes; voltage is 12.54V
30 min: 10.60V
45 min: 10.53V
ONE HOUR: 10.47V

Now - back on the charger.

 

Built this rig. Running fan until battery is exhausted. K1 will drop out at 4V. The purpose is to drain the battery significantly then to recharge it and test it again. As for drop out voltage, I tested with several different resistors until I found one that dropped out at about 4.2V. Used variable power supply for testing. After running 2 hours the voltage has dropped to 10.31 and doesn't show much sign of dropping any faster than normal. Will this battery fully recover? Time will tell.

 

Will this battery fully recover? Time will tell.

It's not going to recover if you keep over discharging. Even deep discharge batteries are only specified for a depth of discharge of around 50%.

 

Thanks dl324. I'll recalibrate and modify.

 

Will this battery fully recover?

Since there is an apparent shorted cell, that would seem highly unlikely.