I have a couple of batteries that appear to have a single cell shorted. For example: I charge one of these batteries and the voltage after charge is 13.5V.
The battery slowly discharges towards 12.7V over time. If I attempt to use the battery with a moderate current draw, the battery drop instantly to 10.5V - 110.V. It's a standard Sealed Lead Acid battery with a AH rating of 35AH.

I am aware that if I continue to charge the battery to 14.4V, then float at 13.5V, the 5 good cells will essentially be overcharged.

I have devices that work perfectly fine with 10V - 11.0V and thought I could alter a charging scheme for these batteries and such as much life out of them as possible.

Is it feasible to bulk charge them to 12V (2.4V/cell) and float them at 11.25V, and lastly operate them down to about 10.0V? Do you think that I would improve their longevity by applying this new scheme?

 

If one cell is shorted and you have been charging the battery like it wasn't for more than a few times then the other cells have been gassing and are most likely severely degraded from electrolyte loss. I would charge to the 5 cell voltage and do a load test at the C/10 rate.

 

I don't know that a load test will tell me anything. I have the batteries and intend to use them until they can no longer operate devices in a specified voltage range. I just wanted
to verify my logic with respect to a new charge scheme and prolonging the "life" of the batteries.

 

I don't know that a load test will tell me anything. I have the batteries and intend to use them until they can no longer operate devices in a specified voltage range. I just wanted
to verify my logic with respect to a new charge scheme and prolonging the "life" of the batteries.

The load test will tell you if the remaining cells are worth the the amount of power it will take to keep them charged, if the actual capacity is 2Ah instead of 35Ah it might be a good thing to know or maybe not.

 

The load test will tell you if the remaining cells are worth the the amount of power it will take to keep them charged, if the actual capacity is 2Ah instead of 35Ah it might be a good thing to know or maybe not.

Your suggestion can have it's uses, but I mainly use the "5 Cell" Batteries to operate a bedside lamp at night. With a Super Bright LED that "requires 12V" it can run fine down to 9V. It's connected to a 555 PWM circuit and I usually have the duty cycle at 50% - 60% with plenty of light. This really is the ultimate test as the battery can last for weeks before needing a recharge. If the battery craps out after only a few days before requiring charging, then I know it time to put it to bed!

It's free energy as I got the batteries from the local dump and charge them via solar methods.

 

I have a similar setup running lights in a shed with a few 12VDC LED lamps. http://www.flickr.com/photos/nsaspook/sets/72157626339532305/show/

Bad batteries can waste a large amount of power by converting energy that normally would be used to charge the plates into a simple ohmic resistance I/R loss. It's sometimes hard to tell if most of the energy is being stored or just being used as a space heater without testing the actual capacity. I guess in your case with "free energy" and small loads the charge efficiency really is nothing to worry about.


http://www.flickr.com/photos/nsaspook/sets/72157626339532305/show/

 

Interesting the Ionic has a bad battery. I discovered on bank of my solar charged batters was also bad. I had 4 ea Trojon T105 6V 225ah flooded lead-acid in series parallel to give me 12V @ 450ah. One bank of two batteries in series went bad. One battery measured 4V and the other one measured a low 6V. The other two in series each measured 6.75V. The interesting thing was the bad batteries were discharging the good ones after the sun quit charging. I disconnected the bad ones and I am now using the good ones.
I also use them to run reading lights at night. I use some RV light fixtures with #1141 bulbs in them. A number of years ago I developed a circuit that eliminates the surge on incandescent bulbs when they are first turned on. My bulbs are lasting a little over ten years. I also used the batterys to run amateur radio equipment.

 

It's tricky to balance out parallel banks of large batteries because the of very low resistance connections required, a difference of a few milliohms can translate to a good fraction of a volt that when charging a paralleled set means one might get a lot more current than the others. I have a 450Ah bank of two strings of 6v GC-2 batteries in series for 12vdc but I use a 300A battery selector to select string 1 or 2 and charge the strings separately.

 

It's tricky to balance out parallel banks of large batteries because the of very low resistance connections required, a difference of a few milliohms can translate to a good fraction of a volt that when charging a paralleled set means one might get a lot more current than the others. I have a 450Ah bank of two strings of 6v GC-2 batteries in series for 12vdc but I use a 300A battery selector to select string 1 or 2 and charge the strings separately.

I agree with you. In my case I knew that the maximum charge current would be about 20A because of the charge controller and that the average max current discharge would be about the same so I hand made some connecting leads with #4 guage wire and lugs that were soldered on. I made sure the leads were the same length and that the connections were clean before connecting. I then placed vasaline on all the tightened connectors. The two batteries that went bad were in use almost 8 years so I don't feel too bad.

 

Wow, 8 years. I hope my cheap COSTCO GC-2 batteries last half that time. BZ

 

It's tricky to balance out parallel banks of large batteries because the of very low resistance connections required, a difference of a few milliohms can translate to a good fraction of a volt that when charging a paralleled set means one might get a lot more current than the others. I have a 450Ah bank of two strings of 6v GC-2 batteries in series for 12vdc but I use a 300A battery selector to select string 1 or 2 and charge the strings separately.

Interesting! I drive a diesel truck that has two starting batteries. One is mounted near the front of the left fender and the other at the rear of the right fender. My batteries last about 4 years.

 

Interesting! I drive a diesel truck that has two starting batteries. One is mounted near the front of the left fender and the other at the rear of the right fender. My batteries last about 4 years.

Starter batteries operate in a different charge/discharge mode than a RE (solar power energy storage) system would. A diesel truck battery would almost never be discharged slowly to 50% of capability every day and then recharged by a limited current source. Starter batteries are designed to deliver high cranking amps where the load almost a dead short and the level of charge is almost always near 100% with a good set of batteries and a working alternator set that provides the DC power when the truck is running.

 

Thanks for letting me know the difference. I hadn't thought about level of discharge. I know turning that engine over really sucks the juice, therefore two batteries.