Battery Series & Parallel Connections

Series & PArallel connections

This article covers series (sometimes called serial) and parallel connections, and how they pertain to batteries specifically.  We provide examples, which apply differently when working with solar panels and inverters.

What Are Series & Parallel Connections?

Series Connection

Series connections are for increasing voltage. Two 3v LiFePO4 cells connected in series would create a 6 volt battery.

Batteries are connected in series by connecting cell 1’s positive terminal to cell 2’s negative terminal, then using cell 1 negative and cell 2 positive as the output terminals.

Parallel Connection

Parallel connections are for increasing capacity, both in terms of amp-hours (ah) and in terms of instantaneous output current.

Combination Series-Parallel Connections

Lorem ipsum dolor sit amet, consectetur adipiscing elit. Ut elit tellus, luctus nec ullamcorper mattis, pulvinar dapibus leo.

Series first or parallel first?

There is a lot of debate about whether series-first or parallel-first is best. The industry standard in both small and large battery packs is to connect cells together in parallel first, however, both types of connections are used successfully by many people. The ‘correct’ choice comes down to the particular situation and the designer’s preference.

If you are using good-quality cells that are relatively closely matched, the likelihood of one cell drifting away from the rest is so low, individual cell monitoring versus group monitoring will not give a great advantage in terms of finding 

Pros & Cons: Series First or Parallel First

Parallel First

Series First

Pro Con Pro Con
  • Simplicity of a single BMS
  • Only one BMS to monitor
  • Easiest to setup
  • Simplest wiring connections
  • Least amount of unprotected balance leads
  • Less components that can go bad.
  • (Possibly) lower price by only having one BMS
  • Must use a high-current BMS
  • Only "blocks" of cells are managed and monitored.
  • Less redundancy (one BMS failure causes full system shutdown)
  • Splitting pack in half for repurposing is difficult.
  • Since bus bars are typically used to parallel cells, it can be difficult to acquire enough busbars for parallel connections
  • Each cell is monitored and managed seperately
  • Redundancy; if one bank goes out, you have a backup
  • You can use lower current BMSs to build up a high-current solution
  • Easy access to a second bank that can be easily repurposed
  • Cost of multiple BMS units
  • More components that can go bad.
  • One BMS shutdown can be hidden by other BMSs, leaving faults un-noticed
  • Multiple BMSs may cost more than one large one.
  • More unprotected balance leads

Pros & Cons: Series First or Parallel First

Parallel First

Pro Con
  • Simplicity of a single BMS
  • Only one BMS to monitor
  • Easiest to setup
  • Simplest wiring connections
  • Least amount of unprotected balance leads
  • Less components that can go bad.
  • (Possibly) lower price by only having one BMS
  • Must use a high-current BMS
  • Only "blocks" of cells are managed and monitored.
  • Less redundancy (one BMS failure causes full system shutdown)
  • Splitting pack in half for repurposing is difficult.
  • Since bus bars are typically used to parallel cells, it can be difficult to acquire enough busbars for parallel connections

Series First

Pro Con
  • Each cell is monitored and managed seperately
  • Redundancy; if one bank goes out, you have a backup
  • You can use lower current BMSs to build up a high-current solution
  • Easy access to a second bank that can be easily repurposed
  • Cost of multiple BMS units
  • More components that can go bad.
  • One BMS shutdown can be hidden by other BMSs, leaving faults un-noticed
  • Multiple BMSs may cost more than one large one.
  • More unprotected balance leads

Pros & Cons: Series First or Parallel First

Parallel First

Pro
  • Simplicity of a single BMS
  • Only one BMS to monitor
  • Easiest to setup
  • Simplest wiring connections
  • Least amount of unprotected balance leads
  • Less components that can go bad.
  • (Possibly) lower price by only having one BMS
Con
  • Must use a high-current BMS
  • Only "blocks" of cells are managed and monitored.
  • Less redundancy (one BMS failure causes full system shutdown)
  • Splitting pack in half for repurposing is difficult.
  • Since bus bars are typically used to parallel cells, it can be difficult to acquire enough busbars for parallel connections

Series First

Pro
  • Each cell is monitored and managed seperately
  • Redundancy; if one bank goes out, you have a backup
  • You can use lower current BMSs to build up a high-current solution
  • Easy access to a second bank that can be easily repurposed
Con
  • Cost of multiple BMS units
  • More components that can go bad.
  • One BMS shutdown can be hidden by other BMSs, leaving faults un-noticed
  • Multiple BMSs may cost more than one large one.
  • More unprotected balance leads