Using a Modified Marine Battery Box
Living in the city lights I need to travel a bit to find dark skies. While some on my local haunts,
such as Withlacoochee River and Chiefland, have AC power available others, like Crowley, don't (at least without a 1,000 ft extension).
Portable 12v power seemed like a reasonable solution. Back in 2003 I considered the commercial astronomy power packs on the market bit felt that their
cost was too high for the small amount of power that they offered. Dew is a big problem in Florida and the dew heaters get a workout. Twelve volt deep cycle
batteries were easy to get locally and all I needed was a box to put it in. Poking around the web I saw some great ideas for building wooden
battery boxes. My concern was making them rain proof enough to handle the Florida monsoons. I decided to start with an $8 marine battery box
(that was the 2003 price. In 2024 about $13) from Wal-Mart and it worked so well I ended up building three of them.
All modifications were made to the removable lids of each box. The basic version has two 12v lighter sockets
each with its own fuse protection (a must!!). For the lighter sockets I chose a marine version because it is rust resistance and has a built-in flip-open cap.
Beside each socket is the fuse holder for that socket. Don't rely on each item plugged into the box has its own fuse. Add the fuses to the box even if they
are inline inside the lid and keep a few spare fuses in the battery box if there's room (I use an old film container). The red rectangles are reflective red tape.
Since I took the inside lid photo I added another lighter socket and fuse to it. One for the G11 mount, One for the ASIAir Plus and one to charge a cell phone
with a small car charger plugged in.
Inside of the lid after 20 years
Inside the lid is a marine power block (you could use a crimp to save some cost) that ties everything together.
I use Outdoor Goop to seal everything and prevent the wires from moving around. I was amazed at how well it sticks to the black plastic of the box.
The 5A fuses may need to be adjusted as needed. If your go-to motors have a maximum combined draw of 5A you would likely want a 6-10A fuse so that you are able
to slew both motors at the same time.
Below is the first lid that I made and it has some bells and whistles. I added a volt meter, On/Off switch and a
red LED and three 12V sockets. Later models used the battery clips as the On/Off and I picked up a battery tester that plugs into the lighter socket
to test voltage. The LED works great, but was never used. It has been in use now for over twenty years without a problem. The photo below is from, 2024.
My lead-acid batteries have ranged from 31 amp hour (ah) to 125ah. The quite heavy 125ah battery fits in the box
but it is a little (1/2") too tall to close the lid completely. The 31ah has enough room left in the box to hold spare fuses, a 3ah charger,
battery tester and a 120v inverter. After a few years of use I like the 65ah battery for one night outings. it keeps the dew heaters and the scope's
drives going all night. The 34ah lead-acid battery has run dry about 1am then the dew is bad and the C11 dew strip is on high. Lithium based batteries
were not an option back then.
In March of 2024 I sent in three 12v lead-acid batteries for recycling and ordered my first LiFePo4
battery and an appropriate charger. The battery is 12.8v 50Ah that weighs 10.6 pounds. I'll be testing it with a motorized trailer pusher that uses a
12v winch motor and, as soon as I have a clear night, running my G11 mount, ASIAir and dew heaters for a night. This battery is claimed to last 10 years
and self discharge much slower than a lead-acid battery. I'll update this once I've had some time to test the battery.
Some batteries power storage is listed in Watts instead of Amp Hours. Use 'Amps = Watts / Volts'
to get the Amp Hours. it is important to use the correct Volts and there will be some loss when the voltage is increased or decreased from the batteries native voltage.
So a 640 Watt battery rated at 12.8v would also be a 50Ah battery. If your go-to mount uses 1.5A and the ASIAir running the cameras and dew heaters used 2.4A then
50Ah (battery) / 3.9Ah (load) = 12.82 hours of maximum use (likely a bit less in reality). Go-to motors, astro cameras and other toys all want to drain your
battery so plan appropriately. Try not to cut the available time too close especially if recharging the battery each day is not easy.
During the hurricane trio in 2004 we lost power for over four days after hurricane Frances. The scope batteries, with a
small 75 watt inverter, kept the air pump going on the fish tank. I did recharge the batteries at a nearby house that still had power. Who would
have thought that astronomy would keep fish alive, maybe Pisces?. Add a car phone charger for field or power outage use.
While I used lead-acid batteries in the past if I needed a large power supply now I would consider a
Jackery or similar power tank.
Check your Amp Hour needs. Alternately, a newer technology like a LiFePo4 12.8v battery could replace the 12v (~13v fully charged) lead-acid battery. Always use the appropriate battery charger.
Avoid AGM batteries unless you want to keep them on a trickle charger all of the time when not in use.