# " How can predict the battery life "

Discussion in 'The Projects Forum' started by mishra87, Jun 20, 2016.

1. ### mishra87 Thread Starter Member

Jan 17, 2016
277
3
Dear All,

I have Li Ion battery lets say 3.7V/1450mAh.

Now what will be the key factor of predicting battery life .
How long it will take to battery become dead and what all the key factors need to determine.

2. ### GopherT AAC Fanatic!

Nov 23, 2012
8,025
6,786
3.7 is a "nominal" voltage. Fully charged is usually 4.2V and check datasheet/instructions of battery for discharge voltage.

The things to consider are current draw (amps) and duration of each change in current.

Your batter "should" last 1450mA for one hour, or (5.2million mA*seconds).

Since you don't have a way to exactly measure the milliamps each fraction of a second and multiply with time and add to find the cumulative consumption, it is best to add a little speaker /alarm when the battery reaches recommended minimum.

Note, the voltage should be measured while the load (motor, light, heater,) is powered.

Jan 18, 2008
6,453
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4. ### Nikhil Bhardwaj 2 New Member

Jun 20, 2016
1
0
Basically there are some factors which are to be considered while determining battery life.
> Battery Chemistry : Li-Ion batteries usually use ferrophosphate, cobalt oxide or polymer as cathode terminal. Lithium iron phosphate (LFP) batteries have lesser energy density than lithium cobalt oxide batteries. so have a look at the battery chemistry and make sure you chose the right battery.
>Charge Current/Charge Rate : This is the most important factor for predicting battery life. Many instruction manuals and datasheets mention the charge and discharge rates of batteries in terms of "C" . However they don't exactly mention what "C" is. C actually stands for the amperage rating of the battery. Since you have mentioned about a 1450 mAh battery, 1450 milliapms or 1.45A of current is 1C for the battery.
So if you charge the battery at 1.45A of current you are charging it at 1C. If the charging current is twice i.e 2*1.45A then the charge rate is 2C and so on. Charging at 2C rate will charge the batteries quicker than 1C but might effect the battery life.
>Charge Discharge Cycles : Make sure when you discharge the batteries you discharge them all the way close to lower threshold voltage mentioned in the datasheet. If this is not done, it will effect the SoC and eventually the life will come down. Do not discharge Li-Ion batteries below lower threshold voltage as doing so might cause explosion or short the batteries. Also do not overcharge the batteries.
> From my experience with batteries I have realized that LFP batteries should not be charged just after discharging. Doing so sporadically changes the battery behavior and brings down their battery life. Once you have discharged the batteries give them some time to settle down (20 minutes is what i observed is good amount of relaxation time) and then start charging.

Hope this post helps you.
Cheers..

5. ### Picbuster Well-Known Member

Dec 2, 2013
818
101
hard to do! the factory defines, in most cases, 1000 load and unloads.
Unloading; linear or with pulses. up to the maximum current or below the spec's.
charging: fast, slow or not repetitively not adhere to the complete cycle.
the temperature and humidity (as temp transmitter) is important.

Keep 1000 loads & unloads but done within the spec's as a good guess.
Picbuster

6. ### crutschow Expert

Mar 14, 2008
20,241
5,731
I think typically they rate a battery at a current draw of 1/10th the mAH rating, so it would be 145mA for 10 hours.
A 1450mA it likely will last less than an hour due to battery internal losses at that current.

7. ### wayneh Expert

Sep 9, 2010
14,990
5,448
The first key factor is to define what you mean by "battery life". Do you mean the time between recharges or the expected lifetime of the battery before you replace it?

The time between recharges is calculated from the capacity in mAh, divided by the current draw in mA. This simple estimate can be refined by adjusting for C, (higher discharge rate shortens life), ambient temperature, and maybe some other factors.

The expected lifetime is far more difficult to predict. Manufacturer's guidelines probably give a best-case scenario.