# How to choose a battery for my PCB board?

I have designed a PCB board for one of my projects. The PCB is about 60*80mm in size. I have done various tests in the lab,and now I will have to install it in the required location. However, I have been struggling to finalize the type of battery to use. I want the whole setup to be compact and not have any moving and detachable parts. The operation of the PCB and my calculations for the battery so far are:

There are two modes of operation for the PCB. They are:

1. Deep-sleep mode –Current consumption is about 1.5mA
2. Operation mode –Current consumption is about 120mA

The PCB operates once in every hour, and stays in operation mode for ~30seconds (or ~0.0084 hours). And the rest of the time it is in deep-sleep mode.

So the average current consumption is:

C=(0.0084*120+0.9916*1.5) mAhr
C≅2.5 mAhr


PCB Operating voltage is between 3.3V and 4.2V. And in the future depending on the battery I can change the Power regulation circuit. The current consumption is measured at 4.2V. (Can I use only this for energy calculation?). Hence the Energy required is:

E=4.2*2.5 mWhr
E=10.5mWhr


I need to choose a battery to power the PCB for about 3000 Hours. So the energy requirement is:

E=10.5*3000 mWhr
E=31500mWhr≅32Whr


If I use a Z V battery of R mAhr rating and assume the power regulator in the PCB is P% efficient, then the energy provided by battery is:

Eb=Z*R*P


Generally, for the better long-lasting performance, batteries cannot be discharged for more than 80% of its energy( So I have learned).

Hence the revised Energy of battery is:

Eb=0.8*Z*R*P


We need a battery of E energy. Assume P=80%.

Eb=E=0.64*Z*R
32Whr=0.64*Z*R
Z*R=50 Whr

If Z=12V, then R~ 4.2Ahr
If Z=24V, then R~2.1Ahr
If Z= 5V, then R~10Ahr
If Z= 3.7V(Typical Batteries) , then R~13.5Ahr


I can see many batteries online which , I think, can server my requirement. However, due to None-Little experience in this field, I am unable to consider the practical aspects. And also most of the batteries for this requirement seems to be little bigger. I am aware of the fact that I need to consider shelf-life of a battery and C rating as well, but don't know how to do it.

Can anyone please suggest me which type of batteries will suit my project well?

I hope all my calculations are correct. If there are any mistakes please consider correcting them.

• A Li-Po cell in excess of 10Ah is about right.One prismatic cell or four 18650s in parallel.
– user16324
Commented Jun 16, 2020 at 10:34
• Will there be losses if I use them in parallel and how about the long-lasting capability? Commented Jun 16, 2020 at 10:53
• No but there are rules about connecting LiPo in parallel and charging them (do a bit of reading!) - they must be balanced first, e.g. connect them via a few ohms, and wait till they are all at EXACTLY the same voltage, before connecting them permanently. Good ones won't lose more than 10 or 20% charge in a year.
– user16324
Commented Jun 16, 2020 at 10:55
• Thanks for your reply. I will definitely look into the rules of connecting them. However,it would be very helpful if you can provide the exact make and model which is trustable as there many online which looks fake and I don't know which one I can trust on. Commented Jun 16, 2020 at 11:41
• @Solen'ya - Hi, There is nothing about the actual PCB (e.g. its layout, material, number of vias, footprints etc.) in your question, as far as I can see. It's all about whatever design you have implemented on the PCB. PCBs on their own consume only (minute!) leakage current - "normal" current is drawn by the components on the board! See what I mean? IMHO your question would sound less strange if you said what your project was (just so we don't have to keep saying "project") and replaced "PCB" or "PCB board" in most places, with the word "project" or whatever name you want. What do you think? Commented Jun 16, 2020 at 13:22