That’s going to be a tough answer.
Li-ion batteries are incredibly variable by use.
- You may note reports that charging from 40% to 80% may only use 10% of a cycle not the 40% you’d expect
- Charging from 0 to 100% may be recorded as 1 cycle by there is the possibility of serious decline when a battery goes to zero
- Then you have the temperature, so someone using the computer in a cold environment and not playing games etc. with keep the battery more ‘healthy’
The battery specs say 100 cycles.
So if the max life of one charge is 21 days then in a year it will have dropped about 20% assuming a full cycle every three weeks.
So in theory it could last 2 or 3 years with and increasing but with a shorted span so only 18 or 19 days after a year etc.
This is very unlikely to work out but you never know.
Equally unlikely is that although 99% of the time I use my laptop plugged in that the ML1220 is going to last a very long time.
An example is I am keeping data on my main battery wear.
- There is a recorded <60 cycles in ten months.
- The specs say 1000 cycles over 2 years for a 20% lost i.e. from 55Wh to 44Wh
At my rate of use I doubt I will use 100 cycles in a year so it could be imagined that I’ll lose 20% in ten years. So incredibly unlikely.
So although there are specs for batteries I have yet to see data on how those claims are made, data that can be verified as user practical.
I will be awaiting the feedback with interest.
NOTE:
There is a post above linking to the data for a Panasonic ML1220 that link is a 404. It seems Panasonic do not make the ML1220 anymore.
Here is a link to the data on my site a PDF
UPDATE:
I have found a data sheet for a Maxell ML1220 which states a cycle life of 1500 if only discharged by 10%.
Also Available on my related site
So according to specs above
a 10% usage and 1500 cycles
a 20% usage and 500 cycles
Extrapolate for usage in the 11th Gen where the ML1220 can only be charged when connected to power
a 30% usage 166 cycles (i.e for 30% or approx 6 hours of use not plugged in) then the cycles may only be 167 i.e. 6 hours of such use every other day for a year
a 40% may provide only 55 days
Sadly it seems there is a discharge of around 0.3mAh which means if you don’t use it before then you have just done a 100% cycle
- 100% it may not recover very well and if it does then you may be lucky to get 10 cycles. Still it could last for 10 x 3 weeks ???