Just a few nuggets that may be useful...
As you can see, rechargeable cells have a lower rated voltage than alkaline cells. But they maintain that voltage better through the discharge cycle than alkaline cells. Forgive me for not digging out the precise data, but if say a rechargeable starts at 1.2v and fails at 1.1v two months later, and an alkaline cell starts at 1.5v and fails at 0.9v two months later in a torch, then you can see that the brightness of the torch is going to be different, and it is hard to tell how much life there is left in the batteries if you don't know which type of batteries are being used.
And if Apple's trackpad requires at least 1.1v per cell to function, and there is no input to tell it what type of cell is being used, then it would not be surprising if the power meter can be misleading.
Apologies for making up the numbers to illustrate the point. I think that the meter is accurate for alkaline cells, but not for rechargeable cells.
Bear in mind that rechargeable cells self-discharge much more than alkaline cells. I would guess that most of the discharge in keyboard rechargeable cells is from self-discharge because the keyboard uses a lot less power than the trackpad. So the cost/hassle saving for using rechargeables in the keyboard is minimal.
And in order to see the right hand pane referred to above, you may need to select the gear at the bottom of the column and choose "show more info", which will also add options in that menu.
I use both recharge battery and alkaline battery, they both work in my way, I found a way to extend the meter (I am not sure the usage life)
When you see the battery power is low. Just take battery out..then re-put in again.
You will see the meter change from 1x% to more maybe 30% or 40%+
But I am not sure it is real effect the life of usage or not
BTW, I buy Sanyo Eneloop battery XX series, it show 100% when I finish recharge and put in keyboard.
Not just 80%+!, that's great. But I need more time to test life of usage.
After I observe the battery life . I can almost say
The rechargable battery (I use apple's NiMH) has some issue about measurement meter of Battery Capacity.
(I think it is cause of it use voltage level as life measurement). NiMH battery is just start from 1.2V, not 1.5V
So NiMH battery will drop it life from 100% to 10% very quickly, almost in few days(even it never reach 100% for some small volume)
But NiMH will keep it in 7~10% for a long time as normal battery.
So Do Not need recharge it when it come to 7%, only recharge for much lower.
Please do not post a variation within a thread as it is less likely to receive the attention you hope for. To write your own question is best policy.
Having said that, I would say that battery strength read outs are notoriously unreliable. Best test would be to insert a couple of brand new quality batteries.
If there is no problem with them, the charger is likely to be at fault.
The battery meter is not very reliable. But it is enough to give a reasonable idea of when to make sure you have a spare pair of batteries handy.
If you use Alkaline batteries, just run them down until the device disconnects spontaneously and then reconnects. That's telling you they REALLY have run down.
If you use NiMh, do the same thing. You should keep a spare pair to avoid downtime. If you recharge pre-emptively when they are not fully dischgarged, you will get the memory effect, which is even worse than an unreliable battery meter. Because it will take some time for each pair to run down, make sure that the rechargeables have a very low self-discharge rate. Eneloop are good.
Personally, I bulk-buy cheap alkalines for wireless thermostatic radiator controls, and replace them once a year when they are about half used. And then I have a big box of part-used batteries for kids' and group-ups' toys.
I use my computer for several hours each day. Using Duracell fully charged batteries, I saw the 'need replacing" warning after a week. I previously used Apple rechargeable batteries but found I usually get about a month with either brand. So, one week was a surprise. I decided to ignore the warning and see how long it would take to get to 5% where I would replace the batteries.
I had a bookmark to this Apple Discussions topic noting battery level reporting was unreliable. In the past, I had automatically replaced the batteries with a backup set on the 15% warning.
I received my first Magic Trackpad warning on 14 April 2014. Level showed as 15%.
• 14 April 2014 - first warning on battery replacement. Level: 15%
• 16 April 2014 - Level: 10%
• 17 April 2014 - Level: 9%
• 22 April 2014 - Level: 8%
• 5 May 2014 - Level: 7%
• 7 May 2014 - Level: 6%
• 12 May 2014 - Level: 5%
Levels shown are from the Bluetooth menu or iStats Menu reports. During the testing period, I saw no degraded performance.
By the way, I recharged the Apple batteries when removed on 14 April, inserting them today shows 92%. A month of waiting for use has it dropped 8%. Charge and then insert, I guess.
The memory effect of nickel-based batteries is something from the NiCd era. Modern NiMH rechargeables do not have any appreciable memory effect, and it's fine to recharge them if they're only half-empty.
The trackpad surely only measures voltage as a proxy for "battery level" and interprets this voltage with the assumption the batteries are alkaline primaries, as Tryitonabreadboard suggested. The percentage reported has little meaning for any other type fo battery.