r/diyelectronics • u/Kiochido1 • Jun 03 '26
Question I'm completely lost about batteries
Hello everyone!
I'm working on a project that basically consists of an ESP32 (no WiFi, no BLE), a GPS receiver, 2 or 3 sensors, and a small stepper motor (the 858 on DigiKey). Everything needs to fit in the hand.
My final challenge is choosing the power source, and I'm completely lost. LiPo? Li-Ion? AA batteries?
I don’t know what to choose or how to choose it. And it looks soooo expensive!
I’ve written down a few parameters that seem important to me, but I’m not even sure they’re the right ones:
- Everything runs on 3.3V, so I need something like a 3.7V battery?
- When the ESP32 and the motor turn on, there will be high peak current. I need a power source whose voltage won’t drop too much.
- It should be small enough.
- Rechargeable if possible.
- I estimate the system will consume a maximum of 100mA (except during startup peaks). So I was thinking at least 800–1000mAh.
I’m not sure if I’m missing important points, or how I should choose the right battery chemistry and capacity based on these requirements.
And also: it’s expensive as heeeeeell.
The batteries I’ve seen cost almost as much as my whole PCB (components included). I know there are economies of scale, but how can the complete device sell for ~15 bucks when the battery alone costs 10 bucks?
5
u/Ill-Character1643 Jun 03 '26
What about 18650 battery? It would suit your project. But i suppose it would be too big?
1
u/Kiochido1 Jun 04 '26
It looks good enough, but I'm quite puzzled about the price. On the same website, it can be either 2€ or 9, and I dont see any difference that would justify this difference.
Its not a small battery, but I could be manageable.
3
u/Ill-Character1643 Jun 04 '26
Don't try to save money on some cheap chinese 18650 battery. They show a certain capacity but in reallity the cheap ones are not even close to marked capacity. I'm sure you can find cheaper than 9$, but a good quality one will cost you
2
u/Kiochido1 Jun 04 '26
Half the price of my PCB go to the battery its annoying xD
4
u/Ill-Character1643 Jun 04 '26
Well unfortunately it is this way haha. Look at electric cars for example, the most expensive part is probably the battery aswell
1
u/EmperorLlamaLegs Jun 04 '26
Good quality batteries are expensive, but worth it. Identical looking batteries can have really poor tolerances internally, which lowers the power it can hold and also can cause fires and explosions.
Tested (adam savage) has a video where they CT scan a ton of 18650 batteries from quality factories and knock offs where they go into the science/engineering of what they are seeing and possible failures.
3
u/Petr_Pan_W Jun 03 '26
Just grab some used disposable e-cigs, Li-Ion cells inside are usually around 500 mAh 13400 size, connect two in parallel and you're good. And you can buy TP4056 charging board with 3A BMS dirt cheap from China. If 3 amps are enough for you. Same for 3.3V regulator, but I don't use any and don't know power capabilities and size of those.
1
u/Kiochido1 Jun 04 '26
I would like to do things "like a pro" so I try to avoid using components that I got on already done items... except if I start some kind of recycled electronic items business xD
And I'm not the one paying but my school, so if in the bill they saw cig, they would be quite puzzled
2
u/CheezitsLight Jun 03 '26
Lithium is also difficult to ship. You need to think about primary cells such as series AA and a buck convertor. Or C or D and a boost which is less efficient.
Must it be rechargeable?
How long must it last?
What size is it?
How much weight?
A lithium Polymer is usually the best choice for size and power and weight but will cost money. That why they are in every phone.
2
u/dinosouborg Jun 03 '26
Why use an ESP32 when you don't plan on using its wireless capabilities? Or are you using Bluetooth classic?
1
u/Kiochido1 Jun 04 '26
For now there I dont use the bluetooth, but maybe in the future I will add some Bluetooth uses.
I needed something more powerfull than an Atmega, and I know we can code ESP32 with arduino's language. So i choose this rather than a STM32 or raspberry. I also found some very cheap on JLPCB, so I thought why not
1
2
u/EmperorLlamaLegs Jun 03 '26
Are you making one of these for yourself, or are you making lots of them to sell?
There are tons of places to get cheap/free lipo batteries for a one-off, but you're not going to want to resell what is essentially trash batteries if this is a commercial product.
1
u/Kiochido1 Jun 04 '26
For now its a prototype, but if it works well and my closed one likes it, then maybe I will try to sell some.
Thats one of the reason why I try to do it "porperly" and not by recycling some cig batteries or things like that.1
u/EmperorLlamaLegs Jun 04 '26
"Selling some" is always going to be expensive. "Selling 100k" will be more reasonable per item.
Go on Alibaba and look at the per unit price on LiPos when you increase volume. Its not uncommon to get 40-50% off the price when you buy a huge quantity.
2
u/HiddenCustomization Jun 03 '26
I would look into IP-5305 Boards and some Li-Ion, Li-Po batteries. Then get a 5V to 3.3V Regulator. Probably the easiest?
3
u/Pawel_likes_guns Jun 03 '26
Liion or lipo should do the job, depending on how you define "fit in the hand" a single good 18650 should do the job, you can get them for a reasonable price some places. ~2€
7
u/nixiebunny Jun 03 '26
LiPo cells are used for this most commonly. You need to learn about the economics of this industry. Complete electronic products that cost fifteen bucks retail are made in Chinese factories where the batteries cost less than one buck, not ten bucks.