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I know that this question won't be too difficult to answer, but unfortunately I couldn't find anything reasonable about it on the Internet.

I have a 1.2V 1500mAh rechargeable battery and want to charge it (without a standard charger, although I have one lying around. I only want to do it for learning purposes.) I know that there are modules like the TP4056 for Lipo batteries and 18650 cells, but I don't know that there is something similar for an AA battery. Can I just connect the battery to 1.2V and limit the current to 150ma? At what voltage is the battery fully charged? I would be grateful for helpful tips or instructions.

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  • \$\begingroup\$ What chemistry is the battery? NiCd, NiMH, or something else? If NiMH, googling "charging NiMH" should get you on your way. \$\endgroup\$
    – ocrdu
    Commented Sep 13, 2020 at 8:38

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I know that there are modules like the TP4056 for Lipo batteries and 18650 cells, but I don't know that there is something similar for an AA battery.

it's not about the form factor (AA), but about the chemistry (NiMH/NiCd?).

Yes, charge ICs for such batteries are available. You'd want to check the offerings of the major power IC manufacturers (Maxim, Texas Instruments, On Semi, NXP,…).

Can I just connect the battery to 1.2V and limit the current to 150ma?

That voltage will be too low to fully charge, so the answer to that question is no.

Usually, when building a "dumb" charger (not a fast charger), you'd enforce a constant current (typically: (battery capacity)/(10 hours)) and just charge for the necessary time.

At what voltage is the battery fully charged?

Doesn't really work like that for NiMH batteries; the terminal voltage depends on the aging state of the battery, kind of. It'll be at least something like 1.41 V, but it really depends.

All in all, NiMH and LiPo and Lead acid batteries need different charging approaches. There's really a lot of (older, because nearly obsolete) application notes by aforementioned IC manufacturers that you can read, which would be better than anyone could write in a short answer. Read them.

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  • \$\begingroup\$ It is a NiMH, so thank you for your aswer. Maybe I will just experiment a bit and to be on the save side just charge with 1.3V and 100ma or so. But now I have some points that I can start a better research with. \$\endgroup\$
    – Michael Brown
    Commented Sep 13, 2020 at 9:19
  • \$\begingroup\$ again, you'd not charge with a fixed voltage, but a fixed current. \$\endgroup\$
    – Marcus Müller
    Commented Sep 13, 2020 at 9:25
  • \$\begingroup\$ Oh, thanks for the tip. I didn't know that yet. So should I better set my lab power supply to a fixed 100ma and have the voltage adjusted automatically?Oh, thanks for the tip. I didn't know that yet. So should I better set my lab power supply to a fixed 100ma and have the voltage adjusted automatically? \$\endgroup\$
    – Michael Brown
    Commented Sep 13, 2020 at 10:00
  • \$\begingroup\$ The charging should be terminated if battery voltage goes too high (check the safe max voltage yourself), or the temperature starts to rise rapidly, or the battery voltage stops rising and starts falling (dV/dt limit). Charging batteries safely and quickly is not simple. Slow charging (14h at C/10) should be quite safe, but after 14h the charging should have a time-out to stop charging. Only extremely slow trickle charging at C/20 can be applied for longer, but not left on indefinitely either. You can find these and similar suggestions by searching for NiMH charging. \$\endgroup\$
    – Justme
    Commented Sep 13, 2020 at 10:27
  • \$\begingroup\$ What Justme said. Also, please read my answer completely, especially the last two sentences. \$\endgroup\$
    – Marcus Müller
    Commented Sep 13, 2020 at 10:32

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