Lifespan of the LiPo battery?

Hi,

Does anyone knows what the lifespan of the LiPo battery is?
I read in documents it would last for 400 cycles (charge & discharge).
But since most boards here use a solar cell the battery never really goes to zero or fully charged.

Thanks.

As a first thought: one cycle is from ‘full’ to ‘empty’, and then charging again to ‘full’.

Lithium Ion batteries do not like to be at their lower and higher cutoff voltage (resp. 3 and 4.2V) The best is to keep them at about 3.8V for storage. The 400 cycles is often a minimum number which will go up if the battery stays at around 3.8V.

It depends on the battery charger IC on your target device, but mostly the battery charging starts when the charge current is larger than a certain preset value. This value is preset by a resistor outside the battery IC. For example: when the battery voltage is at 4.0V, there will be a small current into the battery, if this current is larger than the preset ‘threshold current’, the charging will start.

As for the life span: I couldn’t find research that looked into this (continuous charging of a lithium battery in solar cell applications) so we have to learn from practice here. And ‘end of lifespan’ does off course not mean that the battery explodes but that the capacity will then have degraded to a certain value, as is specified in the battery’s datasheet.