Question Choose the right battery for a little off grid projects with single board computer

[thedighubs]

Good morning dear friends

I am planning a little winter project: a raspberry pi project that - eventually includes off grid aspects.
I am a big fan of the single board computer and I love off grid projects.
However, powering a Raspberry Pi with batteries introduces sometimes little challenges in power management. I need to dive into all that.
That said Batteries have limited capacity, and their voltage can decrease as they discharge, potentially leading to unstable operation of the Raspberry Pi.

I think that I have to choose the right battery type:

We have different types of Batteries that are Suitable for Raspberry Pi

A. Lithium-ion (Li-ion) and Lithium Polymer (LiPo) Batteries

B. Nickel-Metal Hydride (NiMH) Batteries

C. Lead-Acid Batteries


Well these are the ones that come to my mind.

There are various pros and cons:

Pros: some of the above mentioned are inexpensive and capable of delivering high current.
Cons: some of the above mentioned are very heavy and with a lower energy density, more suitable for stationary projects

What would you recommend?

 

[mindless1]

You stated pros and cons but not which of them are relative to your project, so it would be pointless to recommend anything specific, yet.

Another pro/con is # of discharge cycles, for example lead acid won't last long if deeply discharged, but you can overprovision for a larger battery array to avoid as deeply discharging, if the volume and weight aren't an issue.

If you need max discharge cycles, yet can't have the bulk of a massive array of supercapacitors, then consider LiFeEPO4, though it will be the most expensive of all the chemistries mentioned so far. You didn't mention crucial parameters such as runtime or budget, either, making me feel like this post is a bit of a waste of time.

Another factor to consider is the weather, temperature ranges, and also how adept you are at building charge and BMS protection circuits for the more volatile chemistries, and the higher need (requirement) for a charge controller for any lithium chemistry... really any chemistry but the lithiums will fail faster from overcharging, and some will be a fire risk.

Battery voltage decrease isn't really a factor. Along with a BMS in series, you'd want a buck switching regulator to produce the 5V the Pi needs, and it will allow stable voltage all the way down to the minimum input voltage it accepts which is typically a volt or two above the (5V) target output, giving plenty of margin for a 3 x cell series lithium, 12V lead acid, or 8 cell series NiMH, but frankly I wouldn't use NiMH today, not as much going for it as the other chemistries.

You might want to do some web searches for ready made solutions for off-grid powering a Pi, or in a Pi oriented forum, see what other users have thrown together.

If cost is an issue, you can usually find the best prices on things like BMS and buck converters at Aliexpress, though there is that ~month wait for the items to arrive.

 

[Hail The Brain Slug]

You can just buy "UPS Hats" off the shelf that accept 18650 batteries and include buck converters, protections, and bms. This seems like it may be a solved problem to me unless there's something specific about your use case that means you can't use one of these.

There are 2x18650 and 4x18650 models I can find easily, although power on time is an unknown to me. Of course it will vary depending on the cells you choose, but you haven't really shared any details about your needs.

From the bit of reading I've done typically they go with small batteries like this and aggressively utilize RTC to only power on the Pi at specific times as needed to perform whatever duty. Add a small solar panel to help keep the batteries charged when possible.

 

[Red Squirrel]

I would do a 12v lead acid battery and use a 5v regulator to get a clean 5v for the RPI. If it needs to be small, a gel cell like in a UPS would do, if size doesn't matter, get a deep cycle battery like for a boat or RV. You'll get ridiculous long run time and be cheaper per wh than smaller battery solutions. No matter what you go with though make sure there is logic to shut it off if voltage gets too low or you'll destroy the battery.