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#### fubar.gr

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##### Question about battery amp-hour ratings
« on: December 12, 2016, 03:37:42 pm »
Most batteries of any type will have a capacity rating in amp-hours or watt-hours printed on them.

But at what discharge level do these numbers refer?

Eg, Automotive lead acid batteries have capacities ranging from 35 Ah up to 100 or more. Does this refer to discharging the battery from 12.8 Volts to 10 Volts ? Or until the voltage drops to zero?

#### NottheDan

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##### Re: Question about battery amp-hour ratings
« Reply #1 on: December 12, 2016, 04:24:51 pm »

#### NANDBlog

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##### Re: Question about battery amp-hour ratings
« Reply #2 on: December 12, 2016, 05:52:25 pm »
Does this refer to discharging the battery from 12.8 Volts to 10 Volts ? Or until the voltage drops to zero?
It makes very little difference, as 98+% of the capacity will be above 10V. The tolerance of the capacity will result a bigger error.

#### sibeen

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##### Re: Question about battery amp-hour ratings
« Reply #3 on: December 26, 2016, 09:59:11 am »
Like many things in the electrical field you have to be careful and read the spec sheets carefully to do any valid comparisons.

For a standard lead acid battery the amp hour rating of the battery is given as the multiple of amps and hours(Doh). As an example if a battery can supply 10 amps for 10 hours it then gets labelled as a 100A/h battery.  The technical bit is in how long a battery is actually discharged over. There are at least five rates that I've seen used, the 10 hour rate being the most common.  As a battery is an electrochemical device normally the longer the discharge is undertaken the more energy that can be withdrawn for it. A battery that can produce 100 amps for 1 hour (100 A/h) would be expected to be able to produce substantially more if the discharge was extended to 10 hours, so you may see something in the order of 13 amps for 10 hours = 130 A/h.

The rate of discharge used is called the "C" rating, so a battery given as 100 A/h C3 means that the battery has given 33 amps for 3 hours; conversely a battery rated at 50 A/h C10 means 5 amps for 10 hours.

The C10 standard is far and away the most common, but I have seen C1, C3, C8 and C20 also used. The C20 was obviously pulled out by some marketing genius who realised he could get a few extra amp hours out of a battery by extending the discharge time.

#### Rick Law

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##### Re: Question about battery amp-hour ratings
« Reply #4 on: December 27, 2016, 05:10:05 am »
Note also that the capacity depends greatly on the output current.  The SLA I have for emergency has multiple ratings listed: Four different Current and their corresponding AmpHour.

Smf