Electronics > Power/Renewable Energy/EV's

Safe trickle/float voltage for li-ion or NiMH cells?


I know that the ideal way to charge a cell is with a charger that understands the difference charge phases and offers some kind of detection for when a battery is full.
But sometimes you just need a quick hack that works for a hobbyist project..

So I'm wondering if there is a battery chemistry or a safe float voltage that can be used to just make a very simple CC/CV charger made from a voltage regulator and current limiter of some sort. It does not need to charge the battery fully, nor operate the battery at its ideal maximum service life. It just needs to "work" and not catch fire..

Can this be done with either li-ion or NiMH cells, with the voltage regulated to something below what would be considered the normal ending voltage?


for my hobby projects I do the following for NiMH:
1.45V / cell @ 20 deg C
Temperature compensation -3 mV/cell above 30 deg C
Check that in charged state the charge current is well below C/50 .. C/100 (eventually reduce the float voltage)
So a AA cell should stay below 30-50 mA at float voltage
and a AAA cell well below 20 mA continously.

But it is also essential to protect the cells from deep discharge.

A charger for 12 AAA cells from USB can be found here:

here the charging current is limited to 100 mA to stay below the 500mA of the USB port.

In the project you also find a battery monitor to switch off in case of deep discharge.

with best regards



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