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I've bought two packages of low-self-discharge nickel-metal hydride AA batteries, each made by a different well-known battery manufacturer.

Sadly, the datasheets aren't very detailed:

• One datasheet is just a single page long. It says that I should charge the batteries at between 0° Celsius and 40° Celsius. But it says nothing else about charging, let alone trickle charging.

• The other datasheet is two pages long. It discusses charging at a charge rate of 0.1C. It also discusses fast charging at 0.5C or at 1C. But it doesn't mention trickle charging at all.

Let's assume neither brand of cell has any gas-recombination capabilities. When a battery is fully charged, may I trickle charge it? If so, what's the maximum charge rate I may use? I don't want to damage the cell.

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  • \$\begingroup\$ The datasheet of the battery should specify this parameter. Do you have that? \$\endgroup\$
    – Gustavo Litovsky
    Commented Jan 31, 2013 at 20:49
  • \$\begingroup\$ @GustavoLitovsky: • I have two types of LSD NiMH AA cells. Each is made by a very-well-known battery manufacturer. • One datasheet is just a single page long. It says that I should charge the cells at between 0° Celsius and 40° Celsius. But it says nothing else about charging, let alone trickle charging. • The other datasheet is two pages long. It discusses charging at a charge rate of 0.1C. It also discusses fast charging at 0.5C or at 1C. But it doesn't mention trickle charging at all. \$\endgroup\$
    – unforgettableidSupportsMonica
    Commented Jan 31, 2013 at 20:58
  • \$\begingroup\$ I added that description to the question since it's relevant. Can you post the datasheets somewhere? It might help others help you. \$\endgroup\$
    – Gustavo Litovsky
    Commented Jan 31, 2013 at 21:02
  • \$\begingroup\$ @GustavoLitovsky: I'd prefer a general answer, since I may buy other brands of cells in the future. \$\endgroup\$
    – unforgettableidSupportsMonica
    Commented Jan 31, 2013 at 21:09
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    \$\begingroup\$ Next time check the datasheet before buying the product (now why wasn't that obvious?). \$\endgroup\$
    – Olin Lathrop
    Commented Jan 31, 2013 at 21:32

2 Answers 2

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How can you tell if the cell has gas recombination capability?

I don't know of any way to tell without asking the manufacturer. If you know of a way, please tell me: I'm curious. That's not something I've looked into. Behaviour at end of charge may well provide some clues.

Anyway, as for traditional NiMH batteries:

  • The advice from most major NiMH suppliers is that traditional NiMH batteries over about 1800–2000 mAh should not be trickle charged at all. A few suppliers say you may trickle charge at low mA for a time after charging—but only for hours, not days.

  • A few suppliers tell you to trickle charge at C/10. Run away fast from their products.

As for LSD NiMH batteries:

  • LSD cells are tricky. They have lower capacity per size, but this does not prove they're safe to trickle charge. I'd guess that, at rates well below C/10, Eneloop Lite cells are OK to trickle charge, Eneloop standard may be OK, and that Eneloop XX are not OK to trickle charge. For cells which are safe to trickle charge, C/40 sounds like it's probably an OK figure.
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  • \$\begingroup\$ • +1: thank you. • I don't know of any way to tell if a cell can recombine gases. But when you first wrote that traditional NiMH cells can no longer do it, you put doubts in my mind about whether or not the LSD cells I own can still do it. • Dear all: Theoretically, once a cell's reached the end of its useful life, I could slice it in half lengthwise. If I've done so, then can I tell whether or not the cell can recombine gases? If so, how? \$\endgroup\$
    – unforgettableidSupportsMonica
    Commented Feb 6, 2013 at 0:42
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A 2011 paper by Chester Simpson says:

For Ni-MH, most manufacturers recommend that the trickle charge rate not exceed C/40.

It's hard to be more specific without seeing the datasheet.

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