Second laptop battery detected but not used

I have a Lenovo Thinkpad W550s running Hera 5.1.2 and the second (external) battery is being detected but not used. Clicking on the battery icon in the taskbar shows two battery icons, but only one ever discharges while the other remains (mostly) full. I'm assuming it's the external battery that's not being used because I get a max of three hours on battery, when I know that the external battery is much larger than the internal and I used to get up to eight hours on another *nix OS. Issuing `acpi -i` reports the following information, which seems strange:
```
Battery 0: Unknown, 98%
Battery 0: design capacity 3462 mAh, last full capacity 3048 mAh = 88%
Battery 1: Discharging, 0%, rate information unavailable
Battery 2: Unknown, 99%
Battery 2: design capacity 5815 mAh, last full capacity 3784 mAh = 65%
```