# battery life of rechargeable lithium battery

I am trying to determine the life of a lithium rechargeable battery (approximation) before a complete replacement is required. From Panasonic's datasheet, I see that at avg. 10% discharge, it is rated for 1000 charge cycles. The nominal voltage is 3.1V and the capacity is 5mAh. Assuming this is connected in circuit and will remain near fully charged (won't be using it as backup often), what do I need to determine the life of the battery in hrs/years. From Wikipedia, I see that we can do cycles x Ah x nominal voltage to get total energy delivered by battery over its life. I also see from the datasheet that the cell is rated for ~2%/yr self-discharge rate, but don't know how to use all this information to get an idea of how long the cell will last.

I'm not concerned about an exact answer as I'm aware this is a huge area of research, I just want to get an idea of how to calculate approximately how long it will last with the info I provided above along with the things I haven't been able to figure out I need.

This is a Panasonic ML621 Manganese-dioxide on the anode (I think) and Lithium/Aluminum on the cathode (I might have swapped the nodes).

• What temperature will the battery be stored at? Since you are not cycling the battery, most likely, the single most important thing is temperature. – mkeith Sep 28 '18 at 5:11
• For now, assuming 25C is fair as I'm just trying to get an idea of the life. – nichollsg Sep 29 '18 at 16:15
• Reach out to Panasonic. Tell them it is a float application, and will only be cycled a few times. How will the discharge capacity be affected by this type of service? I didn't see anything in the datasheet to indicate shelf life or float life. – mkeith Oct 1 '18 at 6:47
• Most likely it will last for a long time. Years. – mkeith Oct 1 '18 at 6:47