Wiring In Series and Wiring In Parallel
Most House Battery setups use a combination of more than one battery. Some use multiples of the same, large battery types and some use a combination of smaller batteries wired to provide greater amperage. Determining what works best for your boat is a personal choice based on money, space, and location of your house battery bank.
How to wire in what you want is knowledge you need regardless of what setup you choose to install.
Let me start by making one point very clear; NEVER WIRE DISSIMILAR BATTERIES IN SERIES or PARALLEL. The explanation comes later. IF volts, amp-hours, or battery type are different, do not connect them together for any reason. For any set up, only batteries that are identicle should be connected together. Peroid.
Wiring in Series
Battery banks created from wiring in series have the same current capacity (AMPS) as the individual batteries, but the voltage is multiplied by the number of batteries in the series string.
Example; a 6 volt 230 amp-hour battery in series with another 6 volt 230 amp-hour battery = a 12 volt output with 230 amp-hours. Likewise, two 12 volt batteries wired in series will produce a 24 volt output with the same amp-hours as a single battery.
To wire batteries in series, the positive terminal of one battery is connected to the negative terminal of the next, and so on. The bank is then connected to house power in the typical fashion using positive to positive and negative to common ground using a battery switch to isolate the bank.
Wiring in series allows us to use higher amp-hour 6 volt batteries to build our 12 volt systems, or smaller 12 volt batteries to build a 24 volt system.
Wiring in Parallel
Battery banks created from wiring in parallel have the same voltage of the individual batteries, but the current capacity (AMPs) is multiplied by the number of batteries.
Example; a 6 volt 230 amp-hour battery in parallel with another 6 volt 230 amp-hour battery = a 6 volt output with 460 amp-hours
To wire batteries in parallel, the positive terminal of one battery is wired to the positive terminal of another battery, and the negative terminals are wired together.
Wiring in parallel results in a higher current (amperage) for the same terminal voltage.
COMBINING SERIES AND PARALLEL TO BUILD A BANK
In some cases, the best battery bank requires combining a number of 6 volt deep cycle golf cart batteries in series to another set of 6 volt batteries in series to create a 12 volt system, and then wire those banks together in series to create a 12 volt system with a very large amp-hour capacity.
So now the WARNING explained.
In series, two batteries that have the same voltage but different amp-hour ratings will create an issue with the charging circuit so one battery will always overcharge before the other battery is fully charged, creating heat, a fire hazard, and possible damage to the wiring. In parallel, two batteries of different voltage will create a situation where the lower voltage battery will draw power (drain) the higher voltage battery and create a system with low voltage that destroys equipment, shortens the lifespan of all batteries, and creates a possible fire hazard.
BOTTOM LINE: When connecting batteries, always make certain they are are the SAME voltage, SAME amp-hours, SAME type (AGM, GEL, Flooded, etc). NEVER mix a Lithium-ion battery with any other type of battery. EVER.