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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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unforgettableidSupportsMonica
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  • The datasheet of the battery should specify this parameter. Do you have that? – Gustavo Litovsky Jan 31 '13 at 20:49
  • @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](http://en.wikipedia.org/wiki/Battery_charger#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. – unforgettableidSupportsMonica Jan 31 '13 at 20:58
  • I added that description to the question since it's relevant. Can you post the datasheets somewhere? It might help others help you. – Gustavo Litovsky Jan 31 '13 at 21:02
  • @GustavoLitovsky: I'd prefer a general answer, since I may buy other brands of cells in the future. – unforgettableidSupportsMonica Jan 31 '13 at 21:09
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    Next time check the datasheet *before* buying the product (now why wasn't that obvious?). – Olin Lathrop Jan 31 '13 at 21:32
  • @OlinLathrop: • Thank you for the tip. +1. • Why wasn't it obvious? I bought the cells a couple months ago. At that point, I'd never heard any claim that newer NiMH cells couldn't recombine oxygen. And I'm not sure that I even knew then that NiMH battery data sheets available. Oh well. You live and learn. – unforgettableidSupportsMonica Feb 01 '13 at 00:51
  • @unforgettableid I had read that all new NiMH batteries had such catalyst inside of them to deal with a permanent trickle charge and the best way to terminate charging was to trickle and measure temperature. The idea of not having such puts that on its ear. – Kortuk Feb 06 '13 at 03:17
  • @Kortuk: Russell McMahon [writes](http://electronics.stackexchange.com/questions/41641/are-there-any-dangers-to-consider-when-replacing-a-permanent-aa-nimh-battery#41648), "As the typical battery capacity arms-race occurred and [non-LSD NiMH] capacities were pushed up to [...] 2100 2300 [...] mAh the manufacturers looked for more space to fit active material into. Something had to go, and it was the gas recombination mechanism." The document you read that mentioned catalysts—when was it written? – unforgettableidSupportsMonica Feb 06 '13 at 07:34
  • @unforgettableid Sorry, I was not clear, I was sharing that you were not alone in misinformation. [Battery university's article on it is quite clear, also](http://batteryuniversity.com/learn/article/charging_nickel_metal_hydride). They generally need a lower trickle rate, C/20 as the max, and that you should not do that for more than a couple days. Just sharing that your misinformation is somewhat common. – Kortuk Feb 06 '13 at 19:36
  • @Kortuk: I am not always so good at understanding English, and I still don't understand. Russell McMahon writes [below](http://electronics.stackexchange.com/questions/56715/how-fast-may-i-trickle-charge-a-full-lsd-nimh-battery#56843) that usually, nowadays, traditional NiMH batteries should not be trickle charged at all. Do you agree or disagree with him? With kind regards, – unforgettableidSupportsMonica Feb 07 '13 at 06:23

2 Answers2

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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.
unforgettableidSupportsMonica
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Russell McMahon
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  • • +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? – unforgettableidSupportsMonica Feb 06 '13 at 00:42
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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.

unforgettableidSupportsMonica
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Nick Alexeev
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