# Understanding Battery discharge rating

Please find the attached image showing amaron quanta 12 V 100 Ah VRLA battery discharge chart at constant current rating. I am bit confused that how should I calculate the battery capacity based on that.

In the table they shown end cut off voltage like 1.3 V, 1.55 V, 1.6 V, 1.7 V, 1.75 V and 1.8 V and corresponding ampere in table like 5 min, 10 min, ....5 hr, 10 hr, 20 hr etc.

If I simple take 10 hr reading then 1.6 V = 9.72 amp 1.7 V = 9.49 amp 1.75 V = 9.31 amp 1.8 V = 9.26 amp

Out of all this what parameter to be consider in discharge test. Most searches says that it should be 1.75X6=10.5 V is the cut off voltage and related to that constant current to be passed. but if that is the case why manufacturer is giving 1.3 V, 1.55 V, 1.6 V, 1.7 V, 1.75 V, and 1.8 V etc. and current parameter for that. If I take 1.6 V and related to that 9.72 amp as discharge current does it will show different capacity of battery or it will be the same regardless of the cut off voltage and current rating.

• What is your question? I can't see a single question mark. – winny Jun 11 '18 at 11:19
• What you seem to be asking is directly answered in the graph, so we're back to wondering what you are actually asking. It would also help to clean up the messy and confusing English, particularly in the last paragraph where you seem to be finally getting to some point. – Olin Lathrop Jun 11 '18 at 11:23

That table tells you two things.

1) The slower you discharge the battery, the more capacity you'll get. Compare the 20 hour figures, which give more or less the rated 100Ah capacity of the battery, and the 60 minute figures of around 60Ah.

2) The deeper you discharge the battery, the more capacity you'll get. Compare the 1.8v and 1.6v endpoint voltage figures on any column.

Now you get to choose what endpoint voltage you want to use in your application.

The deeper you discharge the battery, the fewer charge/discharge cycles it will deliver before wearing out. Do you want high capacity, or do you want a battery that lasts many charge/discharge cycles? You can't have both.

If you're lucky, the battery data sheet will have a graph or table of expected number of cycles versus endpoint voltage.

A battery like this is quite well suited to an application where you habitually use only 50% of the rated battery capacity, but occasionally need an emergency reserve that is not used all that often. You sacrifice a little bit of battery lifetime for high capacity when you must have it.

• Dear Neil, Thank you for your efforts and very well explanation. I got the idea and understood the table completely. – amit Jun 12 '18 at 12:29