I'm using a GSM device powered by a battery, charged from energy harvesting from a low current source (0 to 200mA, the most of the time 20mA @ 9V.)

To charge the 8000mAh 4.2V battery, I'm using a TP4056 with previous buck (after some tests with buck-boost charger I found this configuration more efficient,) and the device is full most of the time if device works as expected.

Right now the TP4056 chooses when to charge: would it be better if I will force discharge a little bit more before charge? What can be the estimated battery lifespan retaining full battery all the time (with a few charge/discharge?)

Edit: Here are the waveforms of the battery voltage, the current through the battery shunt (charge or discharge), and the gas gauge. waveforms

Would it be any better if I limit (lower) charging current?


1 Answer 1


LiIon battery lifespan killers are temperature and voltage.

What cellphones do, which is stick the battery right next to the hot CPU and charge it to the max, is pretty much the opposite of how to maximize battery lifetime.

In fact, stopping charge at a bit lower voltage will reduce capacity slightly, but you'll get a lot more cycles out of it (table from above link).

enter image description here

If you don't require 100% capacity, this is an easy solution. Note partial charge/discharge cycles as you're doing don't cause "memory effect", they're easier on the battery than full cycles. See link above for lots of details.

  • \$\begingroup\$ Very interesting. In previous photo I showed charge of a high current capability harvest enviroment but most of them has about 30mA charge current, so I cannot go lower than 4V or maybe 3.9V for a charge stopping level I think, but your table shows important lifespan gains with this levels. \$\endgroup\$ Commented Nov 28, 2020 at 11:26
  • \$\begingroup\$ And, what is the behaviour of almost dying battery? I suppose one of this scenarios: It lowers his maximun charge level over the time, lost capacity but voltage curve remains almost the same (discharges quicker), or seems ok until last day when suddenly dies? \$\endgroup\$ Commented Nov 28, 2020 at 11:31
  • 1
    \$\begingroup\$ Gradual degradation, loss of capacity, increased internal resistance \$\endgroup\$
    – bobflux
    Commented Nov 28, 2020 at 12:50

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