I’m designing a new chassis for my main board and was looking at replacing the default battery with a pair of 18v batteries so I can hot swap without loosing power. I plan on using the battery plug on the mainboard so I don’t take up a usb-c port.
I know I’m going to have to use a step down circuit of sorts I just don’t know what the pin out is for the default battery is and how to adapt that to the new batteries. The batteries have their own BMS system so I don’t have to worry about that.
The Framework battery is a 15.4V nominal (4S) battery:
While it’s tempting to plug directly into the battery connector, to me it seems like it’d be a lot easier to just use USB-C PD - if you’re building your own case larger case, you might replace the lost USB-C with an additional de-shelled hub board even?
I was seeking a possibility to replace the battery with a bigger one. Then I found this thread. Thanks for this thread.
Here is just a note for the current Framework battery specs.
Framework | Battery
The 55Wh Battery gets you through a workday on a single charge. This pack is designed to provide up to 80% of its original capacity at 1000 cycles, and is easy to replace if you ever need to.
SKU: FRANBBAT01 Weight: 217.3g Dimensions: 239mm x 6mmx 93mm
While there are operational ranges that need to be respected, laptops (well, all devices that use li-ion batteries) use internal BMS (battery management system) circuitry to make sure that cells are kept leveled/within safe temperature and voltage ranges so matching of cells are minimal (even if they were initially matched, they would have different wear due to position/other factors anyway so you couldn’t depend on that).
I’m asking more from the perspective of: If I have two cells, coming off the same assembly line, same physical dimensions, could one be marked / binned as a higher capacity than the other? Thereby allowing you to sell the “packs” as higher capacity batteries without an increase in physical dimensions?
Li-Ion batteries are generally manufactured with specific chemistry variations depending on their usage. A “high-capacity” blend of lithium substrate may store 2500-3500mAh at 3.65V, it may not be thermally efficient at high C rates whereas a “High-discharge” blend may only store 1000-2000 mAh but have a much lower internal resistance leading to much cooler operation at higher draws. These cells only pass if they are within about 8% of their rated specification. (Both the Cathode and the Anode substrates can be chemically altered to achieve different nominal voltages, different electron densities for higher/lower Ah capacities, resistances for thermal management, etc).
Unlike Silicon based manufacturing, Lithium manufacturing is not really a “lottery” whereby a lucky customer may only get 5% more capacity that may also quickly degrade back into the nominal range of capacities as the battery is conditioned.
TLDR: The only way to increase capacity without volume is a by changing the chemistry of the electrolyte and substrate at manufacturing, and deviations/lottery gains are much smaller than with silicon manufacturing. (Although a less consumer friendly case design could probably push the battery capacity to 70 or 80Wh)