Low current discharge of batteries

calendar

My usual battery tests uses a fairly high discharge current, but in many applications batteries will last for weeks or months with the device on. To get some better data for this I decided to do some low current discharges, i.e. with discharge times up to a few weeks. For this I I will show capacity down to a couple of different voltages.
Due to the time involved I can only do it with a few batteries, other brands may be better or worse.

Content
    AA, Duracell Plus Power AA
    AAA, Duracell Plus Power AAA
    9V, Panasonic Pro Power
    CR2032, Panasonic
    LR44, Renata
    Notes

AA, Duracell Plus Power AA

DSC_3529

Discharge%20capacity%20Duracell%20Plus%20Power%20AA

First battery is a normal AA cell, it can deliver more than 3000mAh at low current, if the connected equipment can work with a low battery voltage.

Discharge%20time%20Duracell%20Plus%20Power%20AA

Here it is with a scale in days. With 5mA it is fairly easy to reach 3 weeks of continuous on time.

Discharge%20Capacity%20Duracell%20Plus%20Power%20AA%20chart

To calculate runtime for some equipment, measure the current consumption and check at what voltage it reports battery empty or dies, then find the closest point in the chart and divide the number with the measured current consumption, that is the estimated runtime in hours.

An example: Device uses 4mA and reports battery empty at 1.2V
The closets match is 5mA and 1.2V, it says 2313mAh, i.e. .estimated runtime will be 2313/4 -> 578 hours -> 24 days.

Another example: Device uses 17mA and reports battery empty at 1.3V
The closets match is 20mA and 1.3V, it says 1523mAh, i.e. estimated runtime will be 1523/17 -> 89 hours -> 3.7 days.

With multiple batteries: Device uses 11mA and reports battery empty at 4.8V, it uses 4 batteries.
First we need the empty value for one battery: 4.8V/4 -> 1.2V, because batteries are used in series current will be unchanged.
The closets match is 10mA and 1.2V, it says 2284mAh, i.e. estimated runtime will be 2284/11 -> 207 hours -> 8.6 days.



AAA, Duracell Plus Power AAA

DSC_3537

Discharge%20capacity%20Duracell%20Plus%20Power%20AAA

The AAA has less capacity, and surprisingly I got same result at 5mA and 10mA (I did the 5mA twice with same result).

Discharge%20time%20Duracell%20Plus%20Power%20AAA

Less capacity also means fewer days.

Discharge%20Capacity%20Duracell%20Plus%20Power%20AAA%20chart

See AA battery on explanation on how to use the table.



9V, Panasonic Pro Power

DSC_4168

Discharge%20capacity%20Panasonic%209V%20ProPower

The capacity is less for 9V, but they can often be used to a lower voltage, using more of the capacity.

Discharge%20time%20Panasonic%209V%20ProPower

Discharge%20capacity%20Panasonic%209V%20ProPower%20Chart

See AA battery on explanation on how to use the table.



CR2032, Panasonic

DSC_7050

Discharge%20capacity%20Panasonic%20CR2032

Discharge%20time%20Panasonic%20CR2032

Discharge%20capacity%20Panasonic%20CR2032%20Chart

See AA battery on explanation on how to use the table.



LR44, Renata

DSC_7767

Discharge%20capacity%20Renata%20LR44

Discharge%20time%20Renata%20LR44

Discharge%20capacity%20Renata%20LR44%20Chart

See AA battery on explanation on how to use the table.



Notes


These table is used when I estimate battery life on the multimeters I test.

I hope to do some more battery types later this year (2019).