Death of a battery

5-14-06  

75 amp hour EverStart battery test done, see below.

This page is about how I revived two weak batteries that I use at the cabin.

Sunnyway 20 amp hour AGM battery. This was the original battery in my Xantrex 400 plus. Since I really never used the spotlight or the air compressor (I can just use a power cord for it anyway), 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).

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 6 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 6 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 is 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.

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