18650 battery question

I read up that it is a 3.7v battery but when fully charged should be 4.2volts.

Would it be safe to charge the battery if its at 3.7volts and charge it to 4.2volts? It's an 18650 lithium rechargeable battery.

I'm sure it would be okay. Just checking with everyone..

3.7V is the nominal voltage. You'll find that the battery operates at 4.2V for a comparatively small amount of time. Yes, assuming you have a charger that senses the voltage of the battery, you can charge the battery from any state, but if you're trying to use the battery as only a 4.2V battery, you won't have much luck and the battery will probably die somewhat soon (lithiums like to be around 50% capacity IIRC).

Yes, with an appropriate charger, you can charge/ "top off" the battery at any point you wish.

They do not suffer from the dreaded memory effect that plagued Ni-Cd batteries and to some extent Ni-Mh batteries. Though it is still somewhat practice to discharge it to zero (battery protected packs) and re-charge every so often. If it is necessary is a good question, however since I do not have a degree in chemistry, I tend to discharge fully every 4-5 charges.

Is there any particular reason you want the battery in the +4v range constantly? A good boost driver will output the same amount of current at all points of a batteries life. Or do you plan on using them in a linear (LM317) driver based laser?

Thank you for the quick and helpful responses. Not sure if the 3.74 volts will be good for the laser or would the 4.2 volts be best?

When I got the 18650 I checked the voltage and it was around 3.8, I read up that 4.2 volts would be fully charged, I just wanted to make sure it wouldn't hurt the battery if I charged it from the 3.74 volts its at now to the 4.2.

What would you all do?