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Is it fine to charge a pile of 8 2 Ah AA NiMH @ 11.6 V 0.5 A serially? They are from the same packaging and were bought only for use as an 8x pack - they were not used for anything else. Im not sure whether NiMHs demand balancing like LiPo.

Is it possible for a certain cell to have an abnormally high voltage - even surpassing its rated voltage while other serial cells have abnormally low voltages across them?

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    \$\begingroup\$ It is usually OK IF THEY ARE USED AS A PACK. If you keep all 8 in series during discharge all the time, you can probably get away with charging them in series also. But if some are more charged than others, or if some are old and some are new, or if they are mixed types, it becomes more problematic. \$\endgroup\$ – mkeith Aug 25 '18 at 3:19
  • \$\begingroup\$ I intend to use it as a pack, in a 8x AA battery holder. \$\endgroup\$ – user33915 Aug 25 '18 at 3:34
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    \$\begingroup\$ Maybe just charge them all individually before putting them together. Should be OK. Keep an eye on temperature the first few times you charge them. Make sure there isn't one or two cells getting much hotter than the others. If so, those cells might have lower capacity than the others. \$\endgroup\$ – mkeith Aug 25 '18 at 3:46
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    \$\begingroup\$ At 0.5 A, that’s questionable over time. Initial use should be fine but if you have any means to lower the current close to maximum voltage, the batteries will have an easier life to self-balance. mkeith’s suggestion is good too, if you manage to sense on the hottest battery. \$\endgroup\$ – winny Aug 25 '18 at 13:37
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    \$\begingroup\$ When charging single batteries, it is usually recommended to use a higher or lower charge rate. Use If you use 0.33C, you will get a relatively strong termination signal when the cell is fully charged. At lower charge rates it may be easier to miss the signal. At 0.1C or below, you don't worry about any termination signal. You charge for 120% of capacity (e.g., 0.1C for 12 hours) and then just stop. So 0.5A is only 0.25C, so that is a "no-man's land" for NiMH. If possible, sense temperature on all the cells, and use dT/dt termination method (google that if needed). \$\endgroup\$ – mkeith Aug 25 '18 at 16:45

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