Battery stuff. Most laptop batteries last 2 years and start deteriorating fast. Why? Because they use lithium ion, and theres THREE things that kill them off.
1. DISCHARGING to around 5% capacity remaining. Thats the first reason they die fast. Mine is set in power saving to hybernate and power down if the batteries reach 15% charge remaining.
2. CHARGING to 100% and worse, keeping them at 100% for weeks, as you use it on AC power. They HATE to be full. So my system is configured to charge the battery to only 85% and when in use on AC, to allow them to discharge to 80% all the time. So they sit at 80% indefinitely.
3. BALANCE. They only seem to balance at CV or when fully charged. So if the batteries never see a full charge they get out of balance. Once a month I charge fully. And then use the laptop and the settings allow it to discharge to 80% and then it goes to AC power autoatically.
I did this on my last laptop. Its battery held FULL capacity in mAh after 5 years of use. So it works. This is what tesla does with the cars battery too for the same reasons.
So if you dont want to murder your lapop of ipad or other gadgets battery set its charging options to use the middle 70% and not the empty or full points.
Set them to do this.
Note: BOTH batteries are sat at 80% charged. And its not charging. And its on AC power.