Which Battery Setup Provides More Backup Time: 2 12V 200Ah or 4 6V 200Ah Batteries?

To determine which battery setup will have more backup time, we need to look at the total capacity of each configuration. Capacity is a crucial factor in determining a battery's ability to provide a consistent power supply over extended periods.

Two 12V 200Ah Batteries

When using two 12V 200Ah batteries, the total capacity can be calculated as follows:

Battery Specifications:

Voltage: 12V Capacity: 200Ah

To calculate the total energy:

Text{Total energy} Text{Voltage} × Text{Capacity} 12V × 200Ah 2400Wh

Four 6V 200Ah Batteries Connected in Series

When connecting four 6V 200Ah batteries in series to create a 12V system, the key considerations are:

Voltage: 6V 6V 6V 6V 24V when connected in series Capacity: 200Ah, as capacity remains the same in a series connection

To calculate the total energy:

Text{Total energy} 24V × 200Ah 2400Wh

Conclusion

Both setups provide the same total energy of 2400Wh. Therefore, the backup time will be the same for both configurations, assuming they are used under the same load conditions.

In my view, as long as both battery setups are combined to get 24V with the same capacity of 200Ah, the backup time will depend on the load that any of the batteries are powering and the affordability of the batteries at your disposal.

Physical and Economic Considerations

For instance, the two 12V batteries combined in series would deliver 24V @ 200Ah. Such large batteries, I assume, are automotive ones, which can be quite expensive and may occupy significant space if used in a stationary application.

On the other hand, the four 6V batteries can be arranged in series to deliver the same capacity but would also be expensive. These batteries can be made into a small battery pack that occupies little space.

Losses and Energy Efficiency

Connecting batteries in parallel is fraught with problems, so the way to compare the two sets of batteries is to consider them wired in series. They both total 24V and the Ah capacity of the two battery stacks is the same, so according to basic theory, they should provide backup under load for the same time.

The variable is the unspecified load and how it is managed. If it is a low voltage load and managed with a switch mode regulator, all is well. If it is managed with a linear, or resistive, regulator, much of the energy may be lost as heat. Energy-efficient, long-duration solutions would be to use the batteries individually to supply backup at, say, 5V (with 6V batteries in pairs) or for 12V individually.

For 5V, the individual 6V batteries would win hands down but come with the disadvantage of the need for downtime.

Safe Parallel Connection

Batteries can be safely connected in parallel if a series diode is connected in the feed from each battery or stack. The load will then be met by each battery or stack according to its ability to meet it. Diodes prevent back feed.

In summary, the choice between the two battery setups depends on the specific requirements of the application, including the load, space constraints, and cost considerations.