NiMH D cells at low drain and 30 degree F

I have an Ozone generator in the refrigerator that actually (against all of the laws of snake oil) seems to actually keep food noticeably fresher (generally veggies). It uses 4 D alkaline cells. The manufacturer says not to use rechargeable cells. Asking them why was not fruitful. I got many months (>6) of life out of a set of batteries. I am guessing that performance at low temperatures is not good on NiMH. I have found some curves for an NiMH D, but nothing showing how temperature affects the capacity/discharge.

The current is fairly low (I don't know what it is). It tells me when the batteries need to be replaced. This is my first set of batteries. When I removed the D cells, they were all sitting a bit less than 1V. Looking at the curves for NiMH, they should stay above 1V until they are pretty much depleted. Potentially working better than the alkaline.

Can anyone provide some insight on using the NiMH in this application? And if a good brand can be recommended if, indeed, it is a good idea.

Eneloop NiMH batteries are good down to -20C, which is far colder than what alkalines will perform at. So, temperature is certainly not an issue with using NiMH batteries. They probably never tested their device using 1.2v cells, but since you've tested your device down to 1.0v, then it should work fine with NiMH.

Get some low-self-discharge cells.

As far as I know, NiMh cells should work better in low temperatures than alkalines. But at that low drain this is not really an issue.

Low self discharge cells should be recommended here, although at that low temperature, self-discharge is slowed down very much anyway. I'd also recommend low self discharge cells since they tend to be more consistent than high capacity cells. Consistency is key here since they will hold up several months on one charge (I'd estimate at least 3-4 if you buy "full" D cells with at least 8 Ah, depending on their actual capacity) and they will be discharged nearly until the end.

The only danger I see in rechargeables here is that they might be discharged completely, at which point the weakest cell might be discharged deeper than the other ones or even reverse-charged, which will not be good for it, so it may fail rather quickly. 1V no-load voltage is actually pretty low for alkalines and means that nearly every last bit of energy was sucked out of them, so their loaded voltage might have been much lower than that before you took them out. It would be similar with NiMh cells, I suppose. To help with that, you might routinely want to recharge them after, say, 3 months (depending on their capacity) before they actually get completely depleted.

Lots of manufacturers say alkalines only for no good reason. Maglite is a prime example here. Yet they work just fine on NiMH. Why do they say this? Who knows. Maybe they want the batteries to leak so that you will buy a new one. Anyway, I see no reason why NiMH shouldn't be a problem. As for LSD vs non-LSD, I don't know that one is better than the other considering both the temperature AND the fact that even current non-LSD batteries self discharge FAR slower than they once did. Regardless, Tenergy makes good NiMH D cells in both LSD and non-LSD variants. Both are good cells. And they are actually fairly inexpensive.

Yeah, I know that... the battery compartment of an old Philips boombox also says "Use only Alkaline and Zinc-Carbon batteries". I think that's to exclude other types of battery (such as Li-Ion) which may have a vastly different voltage at the same form factor, destroying the device in question.

Another consideration is that of runtime... manufacturers recommend whatever will give you the longest runtime, regardless of cost. Especially for lights with "D" batteries, an alkaline "D" has up to 16 Ah as far as I know while the rechargeable "D"'s found in stores often have vastly reduced capacity of only 2-3 Ah and thus would only give a fraction of the runtime of Alkalines. Therefore manufacturers recommend Alkalines for the longest runtime, assuming you will be much happier with your flashlight if you can run it much longer, even if you then have to discard the batteries and buy new ones, vs. having to recharge it much more often, but saving the money for new batteries each time. Shure writes the same about their wireless microphones, at least about those using 9V batteries.

Also I think some manufacturers may have a deal with battery manufacturers supplying them with pack-in batteries at an OEM price, in turn they discourage the use of rechargeables in order to potentially increase the sale of disposable batteries for their suppliers. Not to mention some manufacturers of flashlighs also manufacture alkaline batteries, such as Varta, and I think Maglite once belonged to Energizer, or they are owned by the same parent company, or something like that.

StorminMatt said:

Lots of manufacturers say alkalines only for no good reason. Maglite is a prime example here. Yet they work just fine on NiMH. Why do they say this? Who knows. Maybe they want the batteries to leak so that you will buy a new one. Anyway, I see no reason why NiMH shouldn't be a problem. As for LSD vs non-LSD, I don't know that one is better than the other considering both the temperature AND the fact that even current non-LSD batteries self discharge FAR slower than they once did. Regardless, Tenergy makes good NiMH D cells in both LSD and non-LSD variants. Both are good cells. And they are actually fairly inexpensive.

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