1. What is the difference between series battery connections and parallel battery connections and how do they increase battery capacity and voltage?
Answer: In the SERIES CONNECTION, batteries of like voltage and Amp-Hr capacity are connected to increase the Voltage of the battery bank. The positive terminal of the first battery is connected to the negative terminal of the second battery and so on, until the desired voltage is reached. The final Voltage is the sum of all the battery voltages added together while the final Amp-Hr, Cranking Performance and Reserve Capacity remain unchanged.
2. I would say do not connect in series, doing this as you will double the battery voltage to 24V ( 2 x 12v 75ah) in series = 24V ) but 75AH
The AH rating remains unchanged. You will damage the pump, cables and any controller if you try push 24v through it
Connection in parallel is ok as voltage remains the same at 12V. but you increase the available amp hours.
Answer: In PARALLEL CONNECTION, batteries of like voltages and capacities are connected to increase the capacity of the battery bank. The positive terminals of all batteries are connected together, or to a common conductor, and all negative terminals are connected in the same manner. The final voltage remains unchanged while the capacity of the bank is the sum of the capacities of the individual batteries of this connection. Amp-Hrs, Cranking Performance and Reserve Capacity increases while Voltage does not.
Connecting in Parallel will give you 12V but double the AH rating EG (2 x 12V 75AH ) = 12V but 150AH
Do bear in mind that a leisure battery and Vehicle battery are designed to discharge in different ways. As a rule you are better off running the system from a leisure battery which is designed for longer continuous discharging.
It is well worth mentioning the difference between the Leisure battery and a Vehicle battery.
A car's battery is designed to provide a very large amount of current for a short period of time. This surge of current is needed to turn the engine over during starting. Once the engine starts, the alternator provides all the power that the car needs and slowly recharges the battery. So a car battery may go through its entire life without ever being drained more than 20 percent of its total capacity. Used in this way, a car battery can last a number of years. To achieve a large amount of current, a car battery uses thin plates in order to increase its surface area.
A deep cycle battery is designed to provide a steady amount of current over a long period of time. A deep cycle battery can provide a surge when needed, but nothing like the surge that a car battery can produce. A deep cycle battery is also designed to be deeply discharged over and over again (something that would ruin a car battery very quickly). To accomplish this, a deep cycle battery uses thicker plates.
A car battery typically has two ratings:
CCA (Cold Cranking Amps) - The number of amps that the battery can produce at (0 degrees C) for 30 seconds.
RC (Reserve Capacity) - The number of minutes that the battery can deliver 25 amps whilst keeping its voltage above 10.5 volts
Typically, a deep cycle battery will have two or three times the RC of a car battery, but will deliver one-half or three-quarters the CCAs. In addition, a deep cycle battery can withstand several hundred total discharge/recharge cycles, while a car battery is not designed to be totally discharged.
Fitting a split relay may help boost the leisure battery by a few amps depending on how much driving you do each day. Also ensure you fit the correctly rated fuse to protect the system
These links may be useful
http://www.springltd.co/node/152http://www.springltd.co/node/139 & Battery Basics:
http://www.progressivedyn.com/battery_basics.htmlYou may be best talking to an auto electrician before you consider any of this. Also be wary you are not invalidating your vehicle warranty by adding to the electrical system of the vehicle.