EEVblog #140 - Battery Capacity Tutorial
Why Electrical Engineering Stack Exchange recommends it
Electronics Stack Exchange answerers and commenters point people to it when a question hinges on what battery capacity really means, how it changes with load and cutoff voltage, or how to compare cells in Wh rather than mAh.
Recommended by 4 people across 4 different months, 2014 to 2021.
What it is
Dave Jones of EEVblog gives a half-hour tutorial on battery capacity. It covers amp-hours, mAh, watt-hours, internal or series resistance, temperature effects, cutoff voltages and discharge characteristic curves.
What people said
Recommends James Haigh · 2014-02 · Electrical Engineering Stack Exchange · on “Replacing 6 series AA alkaline batteries with NiMH batteries – how do I compare possible arrangements to optimise usable capacity?”
I watched a video [this video] which though slightly inaccurate in places, I found quite informative (and also rather amusing), and learnt that some devices have such a high cut-off that they “*just piss away*” over half the capacity, so there's still a small possibility that #4 may still be the most suitable, but I seriously doubt it now. Thanks for the info.
Recommends Kamil · 2014-04 · Electrical Engineering Stack Exchange · on “Is my phone battery better / more capacitative than my laptop battery?”
You can't compare different voltage battery capacities in mAh. You have to calculate watt hour capacity (real energy). $$Wh = Ah \cdot V$$ For 2000mAh 3.7V phone battery (example) - capacity is: $$2000 \cdot 3.7 = 7400mWh = 7.4Wh$$ For 11.1V 2000mAh battery it will be $$11.1 \cdot 2000 = 22200mWh = 22.2Wh$$ So energy is different, but constant current capacity are the same. When you buy battery - you pay for energy capacity, not mAh. In reasonable quality devices battery technology is the same, allows the same energy density per mass or size. Some laptop batteries have complicated circuits built in, and you typically pay more per 1 Wh. Watch EEVblog #140 - Battery Capacity Tutorial [this video] f
Recommends user82577 · 2015-08 · Electrical Engineering Stack Exchange · on “How to Calculate the time of Charging and Discharging of battery?”
Dave Jones of EEVBlog fame has several tutorial videos about the subject. EEVBlog #140 Battery Capacity Tutorial [this video] and EEVBlog #772 How to Calculate Wasted Battery Capacity [LINK]
Recommends Bimpelrekkie · 2021-06 · Electrical Engineering Stack Exchange · on “How many amperes can an alkaline AA battery supply?”
You should look in the datasheet of that AA battery and check the discharge curves. That gives you an **indication**. Note that the highest discharge current that is mentioned is 1000 mA = 1 A. That does not mean you cannot discharge with 2 A but realize that the battery's capacity will be less at such a high current. You will get less energy out of the battery compared to a more realistic discharge current of for example 100 mA. You might want to watch this EEVBlog video: [this video]
Cites marcelm · 2016-07 · Electrical Engineering Stack Exchange · on “What is the best way to estimate the power consumption of an Atmega328p microcontroller?”
Because these microcontrollers can operate at 8Mhz and 16Mhz, is the power consumption a linear function of frequency? i.e. does operating at 8Mhz consume 0.2mA * 8 = 1.6 mA of current? First of all, the 328 can run at many more speeds; its maximum clock speed is 20MHz, and at least down to 32kHz is supported, possibly lower. Anything in between is also valid. As for the power consumption, have a look at the datasheet [LINK] , in particular the graph in section 33.1.1 (ATmega328 Typical Characteristics -> Active Supply Current): [LINK] As you can see, the current increases roughly linearly with clock speed. In my experience, there is a "static" component to the power consumption that is adde