Most batteries have about 2000 HP. Generally when we talk about lifespan, its the point at which the battery has lost more than half its initial capacity. This would be 0 HP. It is still usable after this point with reduced capacity, but that will continue to degrade increasingly rapidly.
- Each time you cycle it - that is discharge it all the way down to 0% then back up to 100% - that does 3 HP of damage.
- Each time you partially cycle it - which would be from eg 80% down to 20% and back up to 80% - that does 1 HP of damage.
Also, the battery itself will age naturally, but how fast depends on how charged it is (on average)
| Charge | Damage |
|---|---|
| 100% | 3 per day |
| 90% | 2 per day |
| 80% - 30% | 1 per day |
| 20% | 3 per day |
| 10% | 20 per day |
| 0% | 100 per day |
These are rough figures, and you'll always need some fudging,
So, from this we can do some simple calculations:
- If you use your phone every day, running it all the way from 100% to 0% by the evening, then leave it on charge all night (so 3 HP per day for usage, plus about 2 per day for aging) the battery would last just over a year.
(3 HP + 2 HP) * 365 days = 1825 HP per year. 2000/1825 = 1.0959 years, or * 12 = 13.15 months.
- If you take the same phone with the same routine, but using it less so it still has 20% battery remaining by the evening, and setting it to only charge up to 80%, (so both around 1 HP per day) the battery would last more like 2.5 years.
(1 HP + 1 HP) * 365 days = 730 HP per year. 2000/730 = 2.74 years, or 32.9 months (2 years 8.9 months)
- If you keep the phone on the charger at all times, so its always at 100%, except for once a month when the power fails, that'd be 3 HP per month for usage, and 3 HP per day for aging, and the battery would last about 2 years.
((3 HP * 30 days) + 3 HP) * 12 months = 1116 HP per year. 2000/1116 = 1.79 years, or 1 year 9.5 months.
- If you do the exact same thing, but limit it to charge to a maximum of 80%, that'd be 2 HP per month for usage, and 1 per day for aging, so the battery would last over 5 years.
((1 HP * 30 days) + 2 HP) * 12 months = 384 HP per year. 2000/384 = 5.2 years.
And yes, if you let a battery run down to 0%, it can be completely ruined in under a month.
These are rather pessimistic figures, of course there are far more considerations than this rule of thumb takes into account - storage temperature, operating temperature, quality of the cells, actual charge/discharge termination voltages, rate of charge, rate of discharge, etc, etc. The longest lifespan these calculations will produce is about 5.5 years, and lithium batteries most certainly can last longer than this under more ideal conditions, but this system should provide a minimum expected lifespan.