670G Battery Icon: Green to Red?

I started using the Medtronic 670G several weeks ago, and it has been great. For the first 2 weeks (16 days, actually) I used the 2 alkaline batteries that came with the pump. Then I switched to the lithium batteries that I bought since I have heard that lithium batteries last longer. With the alkaline batteries, the battery icon changed from green to yellow to red over a period of about 8 days, just as expected. However, with the lithium battery, the icon stayed green for about 2 weeks, and then went straight to red, with no yellow period in between. The battery lasted about 2 weeks (which is almost twice as long as the alkaline batteries), and it didn’t tell me it needed replaced until it (I’m assuming) actually did, so there is obviously no big problem, I am just wondering why it skipped the yellow period. Has anybody else ever had this happen (with any kind of battery)?

Lithium batteries are known for a quick drop-off from operational to failure. It is a function of its chemistry. Alkaline battery operational decay is more linear over time.

Here’s the info on batteries taken from page 44 of the 670G User Guide.

It appears that lithium batteries are preferred but will also accept alkaline as well as nickel-metal hydride rechargeables.