Battery

Which is a better inverter battery in terms of performance ?? A 100 Ah – C10 rated battery ?  or A 120 Ah – C20 rated battery ??

The easiest way to explain the phenomenon of the behaviour of lead-acid batteries at various rates of discharge and answer the above question is by using an analogy.

Let me try and explain using the chart as follows:-

A person can possibly A 100 Ah stationary battery 

can discharge at

        Walk for 5 km.               10.00 Amps for 10 hrs.
        Jog for 2.5 km.               16.66 Amps for   5 hrs.
        Run for 1.5 km.               23.90 Amps for   3 hrs.
        Sprint for 0.5 km.               50.00 Amps for   1 hr.

Thus you observe that a person who can walk for 5 km. cannot run or sprint for 5 km. Similarly, a battery cannot deliver the same efficiency when a certain high current is drawn for a short duration as against a lower current over a longer duration.

Thus it is clear that making a battery perform in a slow manner delivers better efficiency than when you try to extract a higher current over a shorter duration.

Now let me explain the behaviour of the same 100 Ah Normal Discharge Performance stationary battery conforming to IS 1651:2013 in technical parlance as follows:-

Sr. No. Discharge Rate Discharge Current Discharge Duration Ah Efficiency
1 C10 10.00 A 10 hrs. 100.00 Ah 100 %
2 C5 16.66 A 5 hrs. 83.30 Ah 83.30 %
3 C3 23.90 A 3 hrs. 71.70 Ah 71.70 %
4 C1 50.00 A 1 hr. 50.00 Ah 50 %

Using the same logic explained above it is possible to rate the 100 Ah stationary batteries at a higher Ah capacity for lower rates of discharge. The following rating also conforms to industry norms and specifications.

Sr. No. Discharge Rate Discharge Current Discharge Duration Ah Efficiency
1 C10 10.00 A 10 hrs. 100 Ah 100 %
2 C20   6.00 A 20 hrs. 120 Ah 120 %
3 C120   1.25 A 120 hrs. 150 Ah 150 %

The examples above generally pertain to stationary batteries used for solar applications.

Based on applications the industrial lead acid batteries are designed and rated differently as follows :-

Battery Type Applications Ah Rating
Stationary Batteries UPS / Inverter/Solar C10
Traction Batteries Motive Power C5
Deep Cycle Batteries Golf Carts / Scrubbers C5

Giving below a chart of Traction Batteries rated at C5 (5 Hr. rate) for 100% efficiency.

Discharge Rate Discharge Duration Efficiency
C8 8 hrs. 108%
C6 6 hrs. 103%
C5 5 hrs. 100%
C3 3 hrs. 88%
C1 1 hr. 66%

Giving below a chart of Deep Cycle Batteries rated at C5 (5 Hr. rate) for 100% efficiency.

Discharge Rate Discharge Duration Efficiency
C5 5 hrs. 100%
C20 20 hrs. 120%

From the above charts, you observe that the same battery at different ratings behaves differently. This is because of the reason that the discharge characteristics vary based on the duration of discharge.

The relationship between discharge current in amperes and duration of discharge in hours is not a linear relationship.

To conclude – when a battery manufacturer says that he is offering a 100 Ah inverter battery rated at 10 hr. rate i.e. 100 Ah @ C10 and another manufacturer says that he is giving a 120 Ah inverter battery rated at 20 hr. rate i.e. 120 Ah @ C20 please understand that the same battery is being offered to you at various rates of discharge.

Which is a better product and who is a better manufacturer is for you to decide?

For more details on batteries and battery manufacturing machines please visit our websites www.unikbatteries.in & www.unikautomation.com 

Ramesh Natarajan Kailad 

Director

UNIK Techno Systems Pvt Ltd 

Pune India

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