Battery hacking - electrical engineers care to comment?

I am now using my L5 as a daily driver. The battery power for daily use is fine, it lasts 8h or so. I also like the bulkiness of the device, I mention this because we will combine these two variables in the next paragraph.

So, they make charge cases for iphones as seen here:

It lets an iphone user have a case and an integrated battery for extended daily use. It got me thinking about what it would mean to buy two more batteries from Purism, wire them up to a usb-c adapter and kind of mount / plug that into an L5.

What I am imagining is something like this:

  1. Take two L5 batteries, and wire them up as if they were in a power bank and plug the usb-c adapter into the L5

  2. Mount the two batteries into maybe a leather case or something that attaches to the L5, doesn’t matter how ugly it is. I can hire someone to make me a leather flip case and it could house the extra batteries as part of the case, I don’t care if it is a bit more bulky I just don’t want to try and mount a power bank.

  3. Basically a short usb-c cable would always be plugged into the L5 during daily use and when I get home I can power charge the L5 and the case mounted battery pack separately.

  4. Are there any electrical engineers here? Can anyone comment on what it would take to rig up the batteries in such a way that they could be used as a battery pack and also be recharged on a daily basis them selves?

Basically, I don’t want to use off the shelf power banks because they are too bulky, wrong sizes, etc. Off the shelf batteries are nice and thin and it seems like wiring up something like this should be straight forward so that it can be packaged into a compact leather case that could be used with the L5.

Can anyone with experience in the area offer insights / comments on how to accomplish this?


I am not an electrical engineer, but I get along well by doing what is described here:

I have used my Librem 5 on plane trips where I was sitting and waiting and then sitting on a plane for a very long time, and was using my Librem 5 the entire time without an opportunity to charge. And all I did whenever the battery got low was to power off the Librem 5 and pop open the back and switch to another battery.

Because I have chargers that can charge the battery external to the Librem 5, it was easy to have 4 full batteries when I started my journey.

So at least in my situation, it does not feel necessary to build some complex additional power apparatus.

My busted former Android phone that never seems to die and has a battery that seems to last a week when idle or whatever, in reality, has a 4000 mAh battery whereas the Librem 5 batteries are 4500 mAh.

I don’t fully understand why but it seems like what holds the Librem 5 back from the super longevity of the battery is in some way software, not hardware. Rather than to construct a complex additional battery apparatus, I wonder if it might be less time consuming to analyze the software of Phoc/Phosh and determine how and where its energy consumption could be optimized.

The software is not not gpu accelerated so a lot of it is getting software rendered on the cpu. That is probably where most of the battery usage comes from. The L5 doesn’t have as aggressive power management as android environments either, so combine the two and the amazing battery life test that I did earlier are more reasonable during the day.

Even if we had fully accelerated drivers (not sure about the actual state of the drivers on the L5, there is some acceleration I guess) software has to support it as well.

Valid point, otherwise, I still want to know for the hell of it.

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I’ve just started a thread on GNOME, which, if we are to trust the author of the articles I mention in my post, could be to blame.

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It is an interesting thought, however, I am actually hoping to run into engineers with the skills to comment on wiring up a battery pack. I literally want the customised battery pack.

I will comment on the software stuff in your thread.

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I would imagine for example putting 2 batteries in parallel (neg to neg and pos to pos with voltage being the same and aporoximate doubling of mAh) and ensuring the usb c connector has the proper polarity prior to insertion on the phone may work accordingly to what you mentioned above. For recharging the bank I would use a fem×fem connector between your charger and charging cable(purism supplied)and battery bank cable…being you have multiple parallel batteries it may tske longer to charge however.

Hope it works out for you…interesting concept.


I would nevertheless mine this out further, as a more practical and a simpler solution. You can’t have looked at every single power bank model in the world.

Putting that around the other way: What are your requirements for a power bank - weight, physical dimensions, capacity in mAh, interface, PD options, …?


This is a good point. Maybe I should look at this again: PurismPower Banks – Purism

Maybe I can get a case built that can hold that and an L5 out of leather or something.

I was looking at the L5 battery, roughly two could be wired up together if we include a controller that I imagine is necessary to control charing and discharging over usb-c. I don’t have any specs in mind, I was wondering if a solution can be designed out from a set of batteries and work outward.

There are a lot of vendors selling batteries including Purism, for example: Replacement Mobile Phone Batteries - BatteryClerk Canada

And a lot of the batteries tend to be 3.7 volts which I have seen used with various custom circuits over the years.

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