You are reading Part 2 of three, Deep Cycle Batteries. This article is about reviving a deep cycle battery that doesn't hold a charge.

Part 1, About batteries

Part 2, Revive batteries

Part 3, Revive batteries through equalization

7-26-10 More on reviving a deep cycle battery. Over the past two weeks, we've been working on two more batteries, EverStart (Wal-Mart) 27DC 115 amp hour marine deep cycle batteries that had lay dormant over the winter and had become sulfated. Using the equalizing method over a period of two weeks, we applied a 6 amp charge to them connected in parallel (230 amp hours total) using the method that I detail in the equalizing a battery page. Last weekend, we had a major storm move through the area and I had the chance to test them under a load condition. Running a small inverter we ran our phone system (cable modem, wireless phones), several CFL bulbs (11 watt and 9 watt) for a total of 105 watts which varied quite a bit depending on the phone usage for a total of around 50 to 60 amp hours per day. Our hydrometer read the charge levels at the end of the first 24 hour period as between 75 and 80% charge. Before the equalization process, a 1 amp load for 1 hour would reduce the charge by 50%, thus leading to the doing the equalizing in the first place. So now I'm doing the same thing on a crapped out EverStart (why did I every buy those things....oh yeah, they were cheap and at Wal-Mart when I needed them) DC24, 79 amp hour battery. This page is by far our most read on the site. That's the good news. The bad news is that we add to it a lot and now it's generated a second page, equalizing your battery bank. This is a much more involved process, contains some dangers, so be careful! Read it here. 7-11-10 Your battery may not be as dead as you think! This page is by far our most read on the site. That's the good news. The bad news is that we add to it a lot and now it's generated a second page, equalizing your battery bank. This is a much more involved process, contains some dangers, so be careful! Read it here. Update: both of the batteries in this article were used for 2 years after they were revived. Both are part of a new battery from recycling at this point, but the methods here did work, extending their lives for an additional 2 years. Each time you discharge a battery either as part of a bank or by itself, several things happen. One, if you discharge it too far (lower than 50%) you will begin to get sulfation, which are deposits on the lead plates in the battery. This occurs when the sulfur molecules in the electrolyte become so discharged that they begin to coat the battery's lead plates. There about 20 reasons this can happen. These are just a few of them: Letting them sit too long between charges (not a problem for any decent off gridder). NOT charging the battery to a full charge! Sometimes it can't be helped. Regular desulfation can be a good thing. Letting the plates get exposed to the air (check the fluid levels). AGM and gel batteries don't sulfate as easily as flooded wet cell batteries but it does happen. If you use an AGM (Absorbed Glass Mat) or a gel battery, you are out of luck if you get sulfation - generally you can't recover them from sulfation. However, read the rest of this article for a method that worked for me. No guarantees, but it worked this one time. This page is about how I revived two weak batteries that I use at the cabin. Be sure to take a look at the temperature compensated charging chart - your hydrometer will give you false readings if you don't take temperatures into account. Most deep cycle batteries do not die, they are pretty much destroyed by their human owners. However, even if you think that it is dead, it's probably not a lost cause. Most deep cycles die because of sulfation which is a build up of deposits on the lead plates in the battery. You can use a commercial desulfator from this company or build your own with actual plans for a battery desulfator Or you can try this: Charge the battery at one of the following rates 2 percent of the RC 1 percent of the amp hours Let me amplify on these methods a little bit. The first method I have used with excellent results. The battery that we tried it on (the Exide deep cycle in this article) was flat and had not been used in 6 months - pretty deep sulfation - and we spent a couple of weeks working it. Do this for 120 hours. Put a load (I'd suggest something like 40 watts - you want to exercise the thing not see how long it will run something) on the battery, repeat several times. If that doesn't work: Another method is to use the charge, drain, refill, charge. Obviously, this next method won't work if your deep cycle battery is one of those maintenance free deals with the little "eye" on the top. If the first method doesn't work, it would make a great A. Boat anchor B. Core for a new battery. So, the second method. Here's how: Drain the battery Replace the electrolyte with distilled water Charge at 4 amps, 13.8 volts until the specific gravity stops rising Drain the battery, wash out the sediment Replace the electrolyte with new. Charge. If the specific gravity exceeds 1.300, start over with step 1. Sunnyway 20 amp hour AGM battery. This was the original battery in my Xantrex 400 plus. While I was taking the Xpower inverter out of the unit, I also grabbed the battery. An interesting aside about the battery: The manufacturer is Sunnyway and this is a 20 amp hour battery. Sunnyway is an Indian battery company and while they have batteries that look exactly like mine, none are 20 amp hour. Xantrex says to order replacement batteries from Enersys, but that is now Exide batteries and don't support Xantrex units. So I'm on my own. Anyways, this battery was used for about 2 years in the Powerpack and I noticed that it was getting weak. I figured that was it, in the words of Scotty on Star Trek, "Aye laddie, she's dead for sure!" Exide EverStart (Wal-Mart) 75 amp hour deep cycle battery. This battery was part of my original bank and is about a year old. Recently while at the cabin, I rewired the bank so all the batteries are connected to one central point (known as a combiner) rather than wiring them as one big 'ol battery. That's when I notice while testing them individually that this one was weaker than the rest. It's always been a problem child but it seemed to perform well. So out it came from the bank and into my electric boat as the power source. 20 amp hour AGM revival: This battery is pretty cool. Small, nice wire connectors and a decent power capacity for running small stuff. I noticed that while it would take a charge, the thing would hold it under load for oh......a minute! Alas I thought it was a goner, so with nothing to lose: Using a battery charger from my days in RC planes, I connected the battery to it. The charger is for Lith-ion batteries which can 'splode if not charged right. It puts out 17.6 volts at 1.12 amps shorted and 14.6 volts under load (varies the power output to the battery). You can get these small chargers at your local hobby shop or online. All you need to do is remove the battery connector that comes with it and hook it up to your little AGM battery. The initial charge on the AGM was 12.45 volts. While it would go to 14.8 volts, it would not hold the charge. First, I connected the charger to the battery for 10 hours. The charged voltage was 12.90 volts. So, I disconnected the charger and let the battery sit overnight. I then connected the charger again for another 10 hours. Now the battery was at 13.60 volts. So I let it sit again. Next I did the charge thing again and after 10 hours, the voltage was now 14.8 volts and at rest it was 12.80 volts. With a load, it worked well. So, I repeated the process. Then, as a test, I ran one of the 12 inch/12 volt circulation fans at the cabin and a 12 volt CF light for 2 days. Not a problem. Next, while I'm here at the house, I'm going to connect a 6 amp load and go from there. 75 amp hour deep cycle: update: after using the method outlined below, I ran 10 watts 6 hours a day off this battery with a 6 amp draw for 1 hour for a total of about 30% of the capacity used. Final charge was 70% so all is good. This battery has always been a little bit of a problem, so I decided to solve this once and for all with a combination of equalizing and slow steady charging. First, I measured the capacity. For a 75 amp hour battery, running my 1 amp test load for just an hour before pooping out was not good. Okay, so I used my Vector Smartcharger at the 10 amp rate and let it charge for several hours until the battery temp. went up as measured from the side of the case. Now I used the dirty little secret of wet cells. I shook it. This releases the bubbles trapped between the plates and mixes the electrolyte in the battery. After letting it rest, I did the same process at 1 amps but for half the time. Next, I let the charger do an automatic charge which starts at bulk, goes to absorption and then hits a trickle charge. The battery has now been running a 12 volt light (5 watts). Starting at 12.81 volts, it is at 12.67 volts and dropping slowly. Next, it's a full charge and a test with my ye' olde 6 amp test draw. ● Email Me ●