How do I increase the capacity or voltage of my battery and system?

The capacity of your single battery cannot be increased from its original capacity. However, strings of batteries can be easily connected to increase a battery bank's voltage or capacity.


To increase the VOLTAGE, you must connect multiple batteries in Series.

Batteries are connected from terminal to terminal, with the positive terminal of one battery connecting to the negative terminal of the next battery.

Series Connections to increase VOLTAGE

Figure 3 - Series Connections to increase VOLTAGE

To increase a battery bank's CAPACITY (amp hours, reserve capacity), connect multiple batteries in Parallel.

Parallel Connections 1      Parallel Connections 2

The connections are correct, but we do not recommend paralleling different types or sizes of batteries, as shown here.

Figure 4 - Parallel Connections

To increase both the battery banks' VOLTAGE and CAPACITY, connect multiple batteries in Series and Parallel.

Batteries are connected from terminal to terminal, with the positive terminal of one battery connecting to the positive terminal of the next battery. All batteries must be of the same voltage. All batteries should be of the same capacity and age.


SeriesParallel Connection for inexperienced installers

Figure 5 - Series/Parallel Connection for inexperienced installers

If more capacity is required, as mentioned above, multiple batteries can be connected in Parallel (the positive terminal of Battery One to the positive terminal of Battery Two and so on).

Only use new and identical batteries. If you connect two 12-volt batteries in parallel and are identical in type, age and capacity, you can potentially double your original capacity. If you connect two that are not the same type, you will either overcharge the smaller of the two or you will undercharge the larger of the two. If you connect two identical, but one is older, you will reduce the life of the new one. When connecting in series or parallel and to prevent recharging problems, do not mix old and new batteries or ones of different chemistries or performance abilities. Cable lengths should be kept short, and cabling must be sized large enough to prevent significant voltage drops. There should be a maximum drop of 0.2 volts (200 milli-volts) between batteries. Many manufacturers restrict you from connecting more than four batteries in parallel.

Connecting batteries in Parallel for experienced INSTALLERS:

It is possible to have more strings in parallel without reducing the battery life or the batteries getting out of balance. General conditions and features that apply for up to 10 strings in parallel are:

  • The same voltage drops must be realized from each string to the end connection (load and ground) regardless if the string consists of one unit (single 2V cells or 6V and 12V monobloc) or several units. This can be achieved by properly choosing cable lengths, cable diameters and arrangement for crosswise connection configurations.
  • The connector cables for the positive and negative terminals of each battery string must have the same length.
  • The minimum cable size for the end connectors of a string is 25mm²/100 Ah of string capacity.
  • The end-connector cables must be placed on a copper bar with at least 100mm²/100 Ah of string capacity with the shortest possible distance.
  • Each string MUST be isolatable with its own circuit breaker.
  • The strings must have the same number of cells.
  • Each string must be exposed to the same heat or temperature potential.

If these requirements are fulfilled, paralleling up to 10 strings is possible. The performance data of all of the batteries have to be applied to the end terminal of each string. By using this parallel string configuration, the system's reliability is increased due to redundancy. Neither battery life nor reliability will be affected if this paralleling is done correctly. Parallel connection of strings with different capacities and ages is possible (the age and capacity of the batteries within each string MUST be the same). The current during both discharge and charge will be split according to the capacity or age of the batteries respectively. Also, the type of lead-acid batteries may differ as long as the required charging regime and voltage (Vpc) per string are guaranteed. Always connect the individual series strings first and check that the different strings are at the same potential before connecting them.

Series Parallel Connection

Figure 6 - Series/Parallel Connection for experienced installers