Good advise for battery systems.
Do not discharge starting batteries below around 90% state of charge. Starting batteries are not designed to sustain DC loads for any length of time (Look how quickly car batteries go flat if a light is left on).
Do not discharge deep cycle batteries below 50% state of charge. By following this rule recharge times will be far quicker, and the longevity and performance of the battery banks will be greatly improved.
For this reason above, deep cycle batteries are the only real choice for inverter operation. Remember that in your DC system, the power inverter will most probably be your greatest low voltage, DC load, however this load is usually for short times only (e.g. using your inverter to run a microwave).
In a normal vehicle, it is not recommended to use an inverter above the 300watt size due to the starter battery installed in the vehicle. To help make your inverter work for longer periods of time, simply run the engine more frequently to keep the battery charged.
For loads greater than 500watts, a properly sized and designated battery bank would be required to run everything in your system (such as lights, fridges, inverter, DC Television just to list a few). Be sure to ensure that you have the suitable recharging abilities to keep the system working effectively (see the Maximising Charge Sources post for further information).
In our experience, the most suitable lead acid batteries for larger systems (average of 50amps+ per day) are the 6-Volt, AGM “Golf buggy” style of battery. Two of these in series up to 12 volts provides the best reserve capacity that you could expect for your independent power system. For a hi-tech solution you can also look at Lithium (LiFePO4) batteries.