Post #515098

2026-02-25 05:21 UTC

mAh/g (milliamp-hours per gram) is a similar unit, but it’s missing the voltage term. We can do a little dimensional analysis here to translate between them. Power = Current * Voltage, so you’d multiply this (CurrentTime)/(Weight) value by the nominal voltage of the cell to get to (PowerTime)/(Weight). So it is essentially still a measurement of capacity, but in terms of current instead of power. Phone batteries are often specified in units of Current*Time (e.g. milliamp-hours), but I’m not sure why.

Replies (2)

@Wispy2891@lemmy.world 2026-02-25 06:37

I’m not completely sure why I think it’s marketing 5000 mAh is much a bigger number than 19 Wh and marketing loves huge numbers Kinda like BMW did with the i3. In 2013 Tesla was selling a model with a 60 kWh battery so BMW had the genius idea to install a 20 kWh battery BUT refer to it as “60 Ah” battery. Tesla introduced the 90 kWh battery? BMW responds with a 94 Ah battery (28 kWh) Newest Tesla has 100 kWh battery now? BMW has 120 Ah battery (38 kWh) “See? Higher number!”, says the marketing And in order to have a comparable range number they had to implement heavy weight reduction techniques like using carbon fiber for the body, negating any cost saving from the smaller battery AND giving the owner a total loss after small collisions as it shatters instead of bending

Open ##518997
@apftwb@lemmy.world 2026-02-25 13:28

> multiply this (Current x Time)/(Weight) value by the nominal voltage of the cell to get to (Power x Time)/(Weight). This is the part that annoys me. The nominal voltage could vary between different batteries. 200Ah/g means different capacity for a 6v battery verses a 48v battery. I'm guessing battery scientists are using standardized nominal voltages for these tests or are seeing the same Ah/g capacity at different voltages (that I may have simply missed in the paper because I skimmed it and I don't claim any deeper knowledge on battery research)

Open ##1567015