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While I am aware of the risk associated with charging Li-ion below 0 °C and that the charge acceptance for a NiMH battery decreases with rising temperature, I am finding conflicting information when it comes to charging NiMH batteries below 0 °C.

Battery University in Table 1 claims that 0°C to 45°C is the charging temp range.

Energizer in Figure 13 claims that the battery will charge at -10°C

Is it possible to charge any NiMH battery below freezing? Is it dependent on the actual battery itself? If it is not able to be charged, why not?

Thanks,

SNM

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    \$\begingroup\$ Charges well at 0 to to 45. Below freezing it's less efficient, but the charging leads to temperature increase internally. What's the actual use case here? \$\endgroup\$ – Passerby Nov 9 '17 at 18:59
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It's not a hard line. The battery doesn't just quit at -0.00001 degrees. It depends on the battery internal temperature and the status of the liquid electrolyte inside the battery. If it is frozen, no chemical reaction can take place. As Energized states, it will charge at 14 degrees F, 10 C, but it has half the normal capacity it would.

See http://www.robotroom.com/Weather-Station-Data-2.html for a empirical look at temperature vs charging results.

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  • \$\begingroup\$ "As Energized states, it will charge at 14 degrees F, [-]10 C, but it has half the normal capacity it would." - This is for discharging, not charging. Can some NiMH be made to charge at these sub-zero temperatures? - Without the use of heating elements \$\endgroup\$ – SNM Nov 9 '17 at 20:02
  • \$\begingroup\$ @snm capacity while discharging at -10 c is lowered. Their charge chart on figure 13 shows it charging at -10 c though. It can charge under freezing, the specifics being how frozen the cell is and how the charging itself can lead to heating, etc. \$\endgroup\$ – Passerby Nov 9 '17 at 22:57
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This is wild speculation, but I suggest that the maximum charge current, and the trickle charge current that the cell can safely handle while fully charged, be reduced at lower temperatures. Possibly proportionally to the low temperature reduced discharge capacity and increased discharge impedance.

There is a catalyst in there to recombine gasses that form during charging, and chemical reactions slow down at low temperatures.

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  • \$\begingroup\$ Wildly speculative answers aren't really much use. \$\endgroup\$ – Transistor Mar 26 '19 at 7:10
  • \$\begingroup\$ I understand, but it's kind of the best there is and that's better than nothing. Have you ever tried to get a reliable answer about the proper float Voltage for lead acid cells? Answers are all over the place. They say "charge at 120mA for 14 hours" on 1.2AH NiMH cells with no warning that over charging at this current will damage the cell. It's even hard to get reliable charging information for normal temperature operation. \$\endgroup\$ – Alex Cannon Mar 26 '19 at 14:55
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Take care! It´s no recommended charge the battery at this temperture. Take note about the specifications of the battery, and the battery charger and the experts in this field (Amperis) Regards

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