Do batteries last longer in Series or Parallel?

Although, batteries connected in Series versus Parallel will offer roughly the same amount of runtime.

It often noticed that series connections provide a higher voltage, which is slightly more efficient for home uses. This simply means that batteries wired in series can last marginally longer than batteries wired in parallel.

But a parallel connected battery will offer you marginally more backup, as capacity gets double when you add the second battery. The only limitation is you cannot run high-end machines, as heating issues will make it inefficient compared to batteries connected in series connection.

Let’s understand the case with an example:

Here we took 12 Volts 150 Ah at C10 inverter batteries to test this down.

Series connection:

In a series connection, you’ll get a total of 24 Volts and 150 Ah of capacity.

If you put a 360 watt load on it, the system will run for 10 hours.

Watt Hours = (12 V × 150 AH) × 2 Units = 1800 × 2 = 3600 Watt Hours.
Backup Time = 3600 Watt Hours / 360 Watts = 10 Hours.

• Series connected batteries do not overheat easily.
• Series connection are easy to learn and to make, higher voltage is good for all kind of setups.
• We can add more load devices, they have a higher output in terms of voltage.
• It’s the single point of failure, if any battery stops working.
• Suitable for large setup with heavy load.

Parallel connection:

In a Parallel connection, you’ll get a total of 12 Volts and 300 Ah of capacity.

If you put a 360 watt load on it, the system will run for 10 hours.

Watt Hours = (12 V × 150 AH) + (12 V × 150 AH) = 1800 + 1800 = 3600 Watt Hours.
Backup Time = 3600 Watt Hours / 360 Watts = 10 Hours.

• Series connected batteries do overheat easily, if you assign more load on it.
• Parallel connection is easy to learn and to make, but higher amps are dangerous to manage.
• We cannot add more load devices, because voltage remains the same.
• If one battery stops working, the setup will work with half backup.
• Suitable for small setup with low load.

In conclusion, there is no such big difference unless you define a load that eliminates one system. Until there is any bottleneck or heating issues, you won’t notice any difference. But for big loads, I’ll recommend series connection.