1. Batteries

2. Battery Systems
When we look at batteries, we look at voltage and capacity.
Lead Acid Batteries (usually) come as 2v, 4v, 6v, 8v or 12v
Depending on the number of 2v cells in the battery
Their capacities are measured in Amp Hours AH, which is measured by discharging them over a period of 20hrs (known as c20). For instance a popular battery – The Rolls S600 6v Deep Cycle Battery is rated at 450AH

3. Battery Banks
When working out Amp Hours (AH) for battery banks, if you have a single battery (let’s say a 12v one) that is rated at 100AH, then if you have 4 of these in series to make 48v, you will have a bank of 100AH at 48v

4. But if you had 4 in parallel at 12v, you will then have a bank of 400AH at 12v
If you multiply the volts by the amps, you will notice they provide the same amount of power i.e. 4.8kW, although not all of this is available, as you must never completely drain your batteries.
We usually recommend a minimum of 400AH for a 24v system, preferably 800+AH if you can afford it.
It depends on what you are going to power from it!

5. Typical 24v system using 4 x 12v Batteries (series & parallel)
The Diagram below is just a rough guide to the layout of a typical system,
always consult the charge controller's manual for actual wiring.

6. Grouping Batteries
In all cases, use identical batteries for each bank, and do not mix types, old with new or capacity ratings, as damage and personal injury could occur. 
Again always use a charge controller & dump load for Air Force1 battery applications.
We recommend for the 48V system, using the Tristar TS45 or Xantrex C40 charge controller. The 12 and 24v systems require a Tristar TS60 or Xantrex C60 

7. Connections Series Connection increases voltage Parallel Connection
increases capacity (AH)
Series & Parallel
increases voltage
& capacity

8. Sizing your Battery Bank
You need to have an idea of the average amount of power you consume in a 24hr period
You then need to know the maximum power required at any one time
List all the electrical items that may be on at the same time, starting with the ones using the most power
Once you have identified the power hungry items, ask yourself whether there is a way of using an alternative item that doesn’t use so much electricity, try to dispense with anything that heats electrically!
Add up the wattage of all the items likely to be used at the same time to give you your maximum demand
This gives you an idea of the minimum size of Inverter you need. I would always suggest going to the next size up!

9. So lets say you use 4kWh per day!
You need to give yourself a battery reserve period of at least 3 days, preferably more depending on affordability
If we use the 4kWh example you will need a 12kWh reserve available from your batteries to keep you going during no wind/solar/hydro days
If you have a steady flow of renewable energy which keeps the batteries topped up, then no problem
Deep Cycle batteries can be discharged by 80%, but we do not recommend that if you want a long life
20% is best, but 50% is acceptable – so you need a 24kWh Battery Bank which is 24V or
We recommend you should always have a backup generator for emergencies. We will discuss this later with Inverters

10. Care of Batteries
One of the most common causes of battery failure is from the lack of MAINTENANCE!!!!
Wet lead acid batteries need to have their electrolyte levels checking regularly, initially with a new set – once a week, then as you get to know your batteries and their behaviour this can be dropped to once a month or whatever experience shows is required.
Fitting hydrocaps will help in this regard

11. Care of Batteries

12. Care of Batteries Measuring Specific Gravity
Modified on: Tue, Mar 18, 2014 at 10:58 AM
Specific Gravity:
The most accurate and direct way to test the state of charge of a battery cell is to determine the specific gravity of the battery electrolyte. The higher the specific gravity of the electrolyte the higher the state of charge. The best way to truly monitor your system over it lifetime is to regularly take and record specific gravity readings.
Unfortunately hydrometers are not easy to use. Testing can be time consuming, there are possibilities for error and safety must be considered. For these reasons we present this bulletin.
Hydrometer Types
Hydrometers come in many sizes and shapes. We recommend a hydrometer with a float, contained in a glass vessel with a rubber bulb to draw the acid into the tube. Stay away from floating colored balls as the extra inaccuracy results in very subjective testing. The hydrometer should give you a numeric reading directly from the instrument. A good hydrometer is accurate to +/ points so could read from The instrument accuracy should be known.

13. Care of Batteries Method of Use
Exact procedures is instrument dependent and this is given as a general procedure and assumes a hydrometer with glass float and body.
Put on eye protection and rubber gloves.
It is recommended to disconnect the battery especially if on a high rate of charge / discharge.
Remove vent cap. Carefully insert the hydrometer into cell, not pushing down on the top of the plates.
Carefully draw liquid into the hydrometer and avoid "bumping" the hydrometer. Be careful the float is not flooded (too much liquid) or sticking to the sides of the glass tube.
Obtain a reading by looking directly at the float.
Repeat steps 3-5 to reconfirm reading.
RECORD the cell number and result.
If it is very warm or very cold correct the specific gravity for temperature. If the ambient temperature is fairly consistent and original gravities are taken when the batteries are put into service temperature correction is not as critical and only necessary if problems arise. Make sure electrolyte is not hot if just taken out of service. Let it reach room temperature.
An easy procedure is to number the cells starting with the positive cell and move from cell to cell towards the negative terminal. If this is part of a preventive maintenance program it is helpful to number the batteries.

14. Care of Batteries
The best way of checking the state of your batteries is to use Specific Gravity
The following shows the approximate state of charge at various specific gravities at 25ºC.
Charged Specific Gravity
100%
75%
50%
25% 0%

15. Care of Batteries Equalization - Corrective
Corrective equalization needs to be performed if symptoms arise such as a constantly running generator (low capacity) or the battery bank will “not hold a charge”. These symptoms are typical of a heavily sulfated battery. If a battery is not being fully charged on a regular basis or limited equalization is performed using a generator sulfation will occur from “deficit” cycling. This undercharge condition can take months before it becomes a major and noticeable problem. This under charge condition is caused when batteries are deficit cycled. The bank receives less of a charge each cycle and starts to sulfate. Eventually the sulfate will cause a resistance to charge and a “false high voltage” reading will occur. The “false high voltage” is measured by the charge controller, which further lowers the charging current to maintain the voltage set point. This further increases the undercharge condition. This is one reason why specific gravity measurements are so important as “false high voltage” readings can be misleading.
Voltage, SG and State of Charge for information on how to correctly interpret voltage readings.
Amperage hour meters can compound the problem and cause people to believe they are returning the correct amount of energy back into the batteries to maintain a good state of charge. Amp-hr meters should be thought of as simply a fuel gauge that does not measure state of charge directly but indirectly. The state of charge is determined by using an equation (peukert's equation). Sometimes there can be fundamental errors with factors used in these calculations. You should always confirm, at least initially, state of charge by taking a specific gravity measurement of one cell when it is thought the bank is fully charged.

16. Care of Batteries Corrective Equalization - Method
Corrective Equalization can take a very long time depending on the degree of sulfation. It is not recommended to equalize with a generator as some generators produce low grade AC that is not properly filtered by the inverter. This is especially true at higher voltages.
If you have hydrocaps remove during equalization.
Set Equalization voltage according to system voltage (see recommended charging parameters). If the bank is severely sulfated or available current is very limited, charge control can be removed or by-passed. Temperature should be monitored very, very closely and keep below 125ºF.
Charge at a low DC current (5 A per 100 AH of battery capacity). If grid power is not available use solar panels or a good DC source when possible. At high voltages, charging with generator can be difficult and hard on the inverter.
Once an hour, measure and record the specific gravity and temperature of a test cell. If the temperature rises above 115ºF (46ºC) and approaches 125ºF (52ºC) remove the batteries from charge. (For temperature measurement choose a center cell, if applicable).
If severely sulfated, it may take many hours for the specific gravity to rise.
Once the specific gravity begins to rise the bank voltage will most likely drop or the charging current will increase. The charging current may need to be lowered if temperature approaches 125ºF (46ºC). If the charge controller was by passed, it should now be used or put back in line.
Continue measuring the specific gravity until is reached.
Charge for another 3 hours. Add water to maintain the electrolyte above the plates.
Allow bank to cool and check and record the specific gravity of each cell. The gravities should be ± or lower. Check the cell electrolyte levels and add water IF necessary.
To avoid this situation it is recommended that a specific gravity reading of one pilot cell is measured and recorded on a regular basis when it is thought that the bank is fully charged. The measurement should be compared to previous readings. If the measurement is lower than the previous reading a longer absorption time and higher voltage setting should be used. Note as stated above, the longer the absorption time and the higher the bulk voltage, the more water will be consumed but less equalization will be required. Note: the specific gravity should rise as the cells use water. Look for trends in the specific gravity over a period of time and make very small adjustments as necessary.