I have an Animas Ping and usually get three weeks to a month out of an Energizer lithium battery. I date them when I put them in the pump to keep track of its usage life. I don't know of another manufacturer of lithium batteries, and I usually buy them in an eight pack and keep them in the refrigerator until they are used.
You might check your pump settings to be sure that your pump is set for lithium batteries. You can get by with an alkaline battery for awhile in the Ping, but its life is much shorter. To check, take out the battery and replace it again. There should be a prompt on the screen that asks if you are using a lithium or an alkaline battery. Select the lithium option, and click ok. Unless your pump is sending excess alarms, pumping excessive boluses or you are using the light a lot, I would think that you should get more than two weeks from a battery.
I think I would keep in touch with Animas on this subject.