How to Connect Batteries in Parallel to Extend Runtime
Extending the runtime on a battery set is best accomplished by increasing the number of batteries in a set. This will also lower the depth of discharge (DOD) and dramatically improve the life of the batteries. Increasing the size of the batteries or reducing the load is impractical in most installations so reducing the DOD and the average daily discharge is the primary goal.
Things You'll Need
- Batteries
- Battery cable
- Class "T" fuses and holders
- DC circuit breakers
- Disconnects
- Battery terminal connectors
- Cable cutters
- Terminal crimpers
- Busbars
- Wire strippers
The Cross Diagonal parallel method
Each pair of batteries is wired in a cross diagonal method. After doing this, the battery pairs are then connected together in the same way as the individual batteries. When using this method, the current from each battery will always go through cables of matching lengths, which results in a perfectly balanced load.
The main reason for using this method is to balance the load on all batteries equally which will greatly extend their life. If battery life is critical or your system is totally off grid, you must balance the load on the batteries.
Another big advantage to connecting batteries using this method is that it gives the ability to temporarily remove each battery without disrupting the circuit.
Several different cross diagonal wiring diagrams and schematics by the originator of the method can easily be found by copying and pasting the below phrases exactly as spelled into any search engine. Be sure to look for the multiple page navigation buttons at the top of some of the sites:
- SmartGauge cross diagonal method
- Most effective series/parallel method
- Linking 4 batteries together
Wire Connection Sequence
- Connect the batteries together using the cross diagonal method (see above for directions for schematics).
- Connect the batteries to the charge controller.
- Connect the PV panels to the charge controller.
- Connect the inverter to the batteries (load).
Battery Connection Tips:
- Always connect the charging source and the loads at the same place.
- Class "T" fuses or DC type breakers should always be used to protect positive wires connecting the batteries to the charge controller and to the inverter.
- If fuses are used, you must install disconnects, although the use of breakers eliminates the need for disconnects.
- Test the function of each circuit as you go along to avoid any serious problems once the power inverter is online.
- Take your time. If you're unsure about a particular step, stop and get help!
- Avoid connecting or disconnecting PV panels while under load by covering them with a tarp or working when the sun is down.
- Use true deep cycle batteries utilizing thicker plates made from solid lead. Avoid using marine batteries that use plates made from a lead powder composite which have a much shorter service life.