WithTheBirds
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Your sample size is too small ‘-pI just did some more testing. Your math is correct but actually drawing 20w per hour is not realistic with modern phones and tablets. They don't charge (draw) at a constant rate and are often drawing much less. So in a real world test I used two fast charging devices, each at or below 20% battery level and it took two hours to get the M2 battery to 50%. Also, I have 4 M2 batteries so if I want to go for a flight and they are charged it isnt realistic to use phones to discharge them.
Seriously- while your playing with numbers have a think about this.
As you have mentioned it is well known that LiION chemistry does experience accelerated capacity loss with time if kept at a high state if charge. Some numbers from battery university indicate that at 100% SOC and 25deg C capacity loss after 12 months might be 20% (compared to 4% at 40% SOC). Lower temp will reduce these numbers and newer battery tech might have improved but let’s take them as a safe conservative reference for some simple maths.
Assume your pack will be good for 150 full charge cycles. It’s a fair number based on user experiences with the phantom drones and reasonable attention to battery care.
Let’s say twice a week you find yourself with a pack your concerned about leaving at 100% so you bring it down to 40% storage level. Over a 12 month period that is 62 charge cycles, over 40% or the pack life. This battery has 24% less available capacity than if you had not bothered to discharge it.
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