Astrophotographers who regularly travel to remote observing sites require a reliable power source to last an overnight imaging session.
Deep-discharge lead-acid batteries typically used in portable power supplies are rated in terms of voltage (V) and current (Ah). Typical ratings are 12V 9Ah. The higher the capacity of the battery, the longer the battery life (e.g., a 12V 9Ah lasts longer than a 12V 7Ah battery). To provide continuous power that will last overnight, a battery must have enough capacity.
In my setup, I have used 4 identical 12 V 9 Ah deep-discharge lead acid batteries connected in parallel, which lasts for about 14 hours.
Connect the batteries in parallel. Attach the battery connector (cigarette lighter socket) observing correct polarity (the central contact point is connected to the positive terminal and the outer contact point is connected to the negative terminal). Insert a switch along the electrical path. Use a thick solid copper wire and then solder carefully all the connection points.
The DIY field battery must be charged with an appropriate charger. The charger should match the voltage (12 V) and should deliver enough current to the battery.
To charge the battery, connect the charger to the battery observing correct polarity: positive to positive (red), negative to negative (black). For chargers with an ammeter, upon connecting the charger to the battery, the meter indicates the amount of current being drawn by the battery at any particular instant. This is very helpful in determining the battery charging status.
I have been using this field battery since November 2011 and have not had problems powering my portable imaging setup. At my current load, the field battery lasts for approximately 14 hours, more than enough power for an overnight imaging session.
Night Sky in Focus
Astronomy and Amateur Radio
© Anthony Urbano (Manila, Philippines)