# Battery Capacity: 9Ahr 12V Power Supply

• haiha
In summary, when using a 9Ahr, 12V battery as a power supply, the "9 Ah" rating typically refers to the amount of useful power that can be extracted from the battery. This rating is based on a discharge time of 1 hour and for smaller currents, the battery will last longer. However, for very small currents, self-discharge may need to be taken into account. It is recommended to consult the battery's data sheet for specific information on discharge rates and voltage drop over time. Additionally, the best current at which the battery will perform will vary depending on the cell chemistry and it is important to not exceed the recommended discharge time for regular usage to maintain the battery's health. It is also worth considering

#### haiha

I am desinging some experiment using a 9Ahr, 12 V as the power supply. I am not sure how many percents of the energy the battery can supply. For example if my experiment consumes a current of 0.1A, then how many hours the battery can be used?

The "9 Ah" rating should be a measure of the useful power you can extract from it not some theoretical maximum.

The rating is usually based on a discharge time of 1 hour, i.e. if it is fully charged the battery will deliver 9A for 1 hour.

There is not likely to be any problem with currents smaller than that, so it will deliver 0.1A for 90 hours.

For very small currents, you also need to take account of the self-discharge rate of the battery (i.e. how fast it goes flat when it is not connected to a circuit) but that is only relevant if the expected battery life is months or years, not a few days as in your case.

Get hold of the data sheet for the Battery. Whilst what AlephZero says is generally true that a 9AHr battery will give 90hrs at 0.1A your particular application may give different results.

The AH rating of the cell is specified at a fixed discharge current "C", the AH are generally constant when the actual discharge is close to "C", but if you are operating at 10 or 20 times "C" you get much less capacity from the cell.

The Battery data sheet will give a number of graphs that show voltage drop off over time at various ratings of "C". You need to check your minimum operating voltage against time for your drawn value of "C".

I have a question. Do we know the current at which the battery gives the best? i mean it has something relating to the AH of the battery.
Thanks

Again it is all contained in the datasheets. IIRC generally at around 0.1C a battery will give maximum energy into the load but can vary quite widely dependent on the cell chemistry.

If you are going to use this device regularly and want to keep the battery healthy, its best to calculate the theoretical time that the battery can produce a useful output, then divide your number by 2 or 3. Do not exceed this time for regular useage. The reason why is because you are using a lead acid battery. It is a fact that lead acid batteries will die much faster if you do deep discharges vs shallow discharges.

Look for 'deep discharge' or 'marine use' batteries rather than regular car/truck type. These are designed to allow you deplete them by upto 90% without damage, most car/truck types can only be discharged to around 50%, although they can supply much higher current for short periods - needed for starter motors.

## 1. What does "9Ahr" mean in "Battery Capacity: 9Ahr 12V Power Supply"?

The "9Ahr" refers to the amp-hour rating of the battery, which is a measure of the amount of charge the battery can hold. In this case, it means that the battery has a capacity of 9 amp-hours.

## 2. How is battery capacity measured?

Battery capacity is typically measured in amp-hours (Ah) or milliamp-hours (mAh). This is a measure of the amount of charge a battery can hold and is determined by testing the battery under specific conditions.

## 3. What does the "12V" mean in "Battery Capacity: 9Ahr 12V Power Supply"?

The "12V" refers to the voltage of the battery. Voltage is a measure of the electrical potential difference between two points and is an important factor in determining the power output of a battery.

## 4. How long will a 9Ahr 12V battery last?

The lifespan of a battery will vary depending on how it is used and maintained. However, based on its capacity of 9 amp-hours, a 12V battery could theoretically provide 9 amps of power for 1 hour, 4.5 amps for 2 hours, and so on.

## 5. Can a 9Ahr 12V battery be used in any device that requires a 12V power supply?

No, the battery capacity and voltage must match the requirements of the device it is being used for. Using a battery with a lower capacity or voltage could result in insufficient power supply or potential damage to the device.