This should be fairly easy to assemble yourself. There’s two things
to consider to make up a useful design, the lamps and the size of the
battery you’ll need.
For the lamps, check with a good lighting store, a discount auto
parts catalog (perhaps JC Whitney), and with a recreation vehicle
dealer to find lampholder designs that would work for your situation.
Keep a record of voltage and wattage needs of each lamp. Once you
determine how many you’ll need, you can add up the total wattage.
Now for the battery selection - the total current to run the lights
is found by dividing the total wattage by the voltage. For
instance, if you need nine lights at 32 watts each, that’s 288 watts
of power required. If it’s a 12 volt system, you will be drawing
288/12 = 24 amps of current to keep the lights at full brilliance.
Batteries are rated by voltage and by ampere-hours of capacity. To
run the above lights, you need a 12 volt battery. These are very
common. If you go with a 24 volt lighting system, you can use two of
these batteries in series.
The capacity number (ampere-hours) will tell you how long you’ll be
able to run your lights on a fully charged battery. Basically, if
the example system of 9 lights requires 24 amps of current and you
want to run the lights for 5 hours, you will require a battery with
at least 24 x 5 = 120 ampere-hours of capacity.
New batteries will be able to deliver their rated capacity, but as
they age, they won’t last as long. This same principle applies to
many things. So you might want to look for a battery with extra
capacity. However, more capacity means a heavier battery to carry
around and a more expensive piece to buy.
One other note, batteries come in two basic types - floaters and deep
cycle. Floaters are used in cars and trucks. They will not perform
well for your lighting application. Deep cycle batteries are used in
golf carts and fork lifts. They’re made to provide heavy and steady
power until they’re exhausted. You can try a car battery, but a deep
cycle will be much better. And yes, they are more expensive.
Finally, batteries don’t last long if they’re left uncharged. You
can ruin a floater car battery if you discharge it all the way and
leave it for a day without recharging it. Plug your batteries in as
soon as you get to a source of power.