Problem Solving a Deep Cycle Battery

In my last post I discussed the expensive prospect of solar power, We bought a generator to power our one big power suck. Beyond that, we need just a little bit of electricity to run a light and a fan. Often, the breeze at the cabin is so nice that a fan is sufficient to keep it cool for sleeping. Sometimes, we need to run an electric power tool or charge a computer.

One 12V deep cycle battery should do it. I bought a battery, a solar trickle charger, and a DC/AC power converter. Assuming the battery was sold to me with a full charge, the trickle charger would keep it topped off as I used it to run one light for a few hours, a fan all night, and a weed eater for about an hour.

Mysterious Issue with the Battery

Day one with my battery set up worked great. I was able to weed eat the entire cabin fence line. I powered a shop light that doubled as a porch light, and I ran a small fan all night. The set up was simple.

The power converter has two 110 outlets and one USB outlet. I use one plug at at a time. If something goes awry, the converter will sound an alarm. By about 10 a.m., the morning after running the fan all night, the alarm sounded.

If I did my math right, this battery should give me 80 amp hours if it's fully charged. I got about 12 amp hours. Either I really miscalculated my power usage, or this battery was not fully charged when I bought it.  Because the converter instructions state that the alarm sounds when the there's an overcharge, a drained battery didn't really make sense. I turned everything off and put the solar trickle charger on the battery. It looks like this:

At optimal performance this 6 watt solar panel will drip electricity into the battery without overcharging it. If I wanted to totally charge my battery with this little panel, it would probably take months. Like - the entire summer - while we melted away in the night.  My hope was the solar panel simply doing it's job of topping off the battery because my alarm was due to something else.

Please Be Something Else...

We had to go back to Austin, so I couldn't really top off the battery all day, and then give it a whirl for another night. I packed everything away until this past weekend. I optimistically pulled out the battery and converter and tried to power the fan. The alarm went off. We slept with minimal air movement. Fortunately, it got pretty chilly overnight, and we were fine.

The next morning, I tried to power the shop light. If the battery was fine, the light would run. Hell no. The alarm went off. Clearly. This battery came mostly drained.

Most people would pack up the battery and take it back to the store. I was 90 miles away from the store. So I decided to give it a charge with the generator. Tammy ran to Giddings and picked up a battery tester; which of course, displayed "Lo" on the LED screen.

If my optimistic math was correct, the generator would charge the battery in about 2 - 3 hours.

That didn't happen. "Lo" never changed to "60%"; although it would quickly flash an exciting "90%" right when I plugged in the tester. I don't trust that. In fact, upon closer inspection, my handy battery charging feature on my generator isn't much more than a trickle charger on steroids. 

Right under that arrow is the number "8." As in 8 amps. As in not particularly powerful charger. As in a whopping 96 watts of charge. I have no idea how much power is in my battery, but I charged for about 4 - 5 hours. I guess I'll make a trip to an auto parts store and see if they can give it a true test and charge for me the next time we're at the cabin. I'll let you know how it goes.