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Old 11-02-2021, 17:12   #1
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Recharging an alkaline battery pack

Hi all,

I have a decent old LED spotlight which is powered by a 4.5 volt, 4000 mAh battery pack.

I’ve lost the AC wall adapter and the company that made it are not really sure what voltage the adapter was for that model (8 years old).

So, I did some searching and I cannot seem to find clear instructions on charging alkaline batteries. (Yes, this is the rechargeable sort.)

Can anyone point me at something that can tell me how to charge these things?

I am kinda hoping a 5 volt USB power source is a workable solution.

Matt
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Old 11-02-2021, 23:13   #2
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Re: Recharging an alkaline battery pack

You could try charging the battery at a very low constant current say 20mA through a resistor from your house batteries with a zener or multi diode shunt or a combination of both to ground between the battery terminal and ground to limit the maximum charge voltage.

Doing the E = IR thing on say 13.6 - 4.5 = 9.1V/0.02A = 455 ohms and 9.1V x .02A = .1 something A so a 430 or 470 0hm 1 watt resister should do it.

Dropping 5V at 20mA gives 5 x .02 = 0.1 watts.

I charge my small SLA battery this way and it does not matter if I forget to take it off charge for a couple of days.
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Old 12-02-2021, 02:09   #3
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Re: Recharging an alkaline battery pack

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Originally Posted by RaymondR View Post
You could try charging the battery at a very low constant current say 20mA through a resistor from your house batteries with a zener or multi diode shunt or a combination of both to ground between the battery terminal and ground to limit the maximum charge voltage.

Doing the E = IR thing on say 13.6 - 4.5 = 9.1V/0.02A = 455 ohms and 9.1V x .02A = .1 something A so a 430 or 470 0hm 1 watt resister should do it.

Dropping 5V at 20mA gives 5 x .02 = 0.1 watts.

I charge my small SLA battery this way and it does not matter if I forget to take it off charge for a couple of days.
That sounds like a good scientific approach.

What do you think about just hitting it with 5.2 volts from.a USB Jack?
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Old 12-02-2021, 05:07   #4
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Re: Recharging an alkaline battery pack

Whenever my dive light chargers die, I just buy a generic RC charger. They can be configured to charge multiple chemistries and cell counts. Often they will also auto detect.
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Old 12-02-2021, 05:52   #5
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Re: Recharging an alkaline battery pack

The details you need are the charge rate and time.

Due to the alkaline batteries higher internal resistance and tightly sealed you need to charge them at low current. If they charge too fast they will leak or explode.

So the question is, dose the pack have some electronics in it to limit current or do you need a charger that will limit the current?

Here is like one of the few links I found on the topic

https://www.best-microcontroller-pro...y-charger.html
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Old 12-02-2021, 05:59   #6
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Re: Recharging an alkaline battery pack

I’d just replace the RAMs with regular primary alkaline batteries.

“... Tests performed by Cadex on 'AA' reusable alkaline cells showed a high capacity reading on the first discharge. In fact, the energy density was similar to that of nickel-metal-hydride. After the battery was fully discharged and recharged using the manufacturer's charger, the reusable alkaline settled at 60%, a capacity slightly below that of nickel-cadmium. Repeat cycling in the same manner resulted in a fractional capacity loss with each cycle. The discharge current in the tests was adjusted to 200mA (0.2 C-rate, or one fifth of the rated capacity); the end-of-discharge threshold was set to 1V/cell ...”
More https://batteryuniversity.com/learn/..._have_a_future

‘Pure Energy’ Data Sheet
"... Pulse Charge of XL RAM requires intelligent charger with a special charging algorithm..."
https://aphnetworks.com/review/pure_.../xlaaa_tds.pdf

Charging Alkaline Batteries
https://michaelbluejay.com/batteries...alkalines.html
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Old 12-02-2021, 10:23   #7
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Re: Recharging an alkaline battery pack

Here's a possible approach:
- Can you open the pack?
Do you see electronics per the suggestion above. That would tell you how smart the charger needs to be.

- Can you replace the cells and do you have access to a battery store that rebuilds battery packs? (Probably either 3 or 6 AA cells with wires soldered between them.)
If they're easily to replace, I'd try to replace them with Ni-MH cells such as Enloop-Pro which maintain their charge during storage.
In any case the battery store can recommend a charger and test the batteries to see if they're worth keeping.
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Old 12-02-2021, 11:18   #8
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Re: Recharging an alkaline battery pack

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Originally Posted by GILow View Post
That sounds like a good scientific approach.

What do you think about just hitting it with 5.2 volts from.a USB Jack?
Some of those things put out a couple of amps which, if you don't have a charging end point voltage, may damage the batteries and even swell them up and burst them.

I've not considered them as truly rechargable so have no experience of actually having done so but the very small current and fairly precise voltage limit tends to prevent anything too exciting from happening.
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Old 12-02-2021, 15:21   #9
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Re: Recharging an alkaline battery pack

Rechargeable alkaline batteries were only on the market for a short time, for the reasons GordMay pointed out. If you really wanted to keep this light then you would be better off fitting a battery holder in place of the current battery pack and fill it with low-self-discharge (LSD) NiMH batteries, such as Eneloops or Imedions. Then charge these in an external charger. Or better yet fit Li-Ion batteries if you want to tackle that.

Personally I would say that it is time to move on. I have flashlights that probably put out more light for a longer time than what you likely have. The new LEDs (e.g. XHP70) can put out 3700 lumens and the 21700 Li-Ion battery can have 5000mAh capacity; I have a ThruNite T2 with those parts and it can easily fit in any pocket, and the design is just about perfect (if you like side switches). https://thrunite.com/t2/ I also have a Wowtac A5 using the same LED and a 26650 battery (also 5000mAh); it is a little shorter and fatter. WOWTAC A5 3650 Lumen - WOWTAC Official Store There is no need for a large old spotlight anymore.

[Both of these flashlights have internal charging with a USB socket, although the batteries can also be charged externally on the Wowtac. The included battery on the ThruNite is special and won't fit other devices, but it can be replaced with a standard battery.]

Greg

[21700 = 21mm diameter x 70mm length, 26650 = 26mm dia x 65mm length]
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Old 12-02-2021, 20:31   #10
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Re: Recharging an alkaline battery pack

Don't know if they still stock them but I have an Eiger electrical LED hand spotlight I bought from Bunnings. About $25 when I bought it in 2017. Charges from a micro USB. I've had a number of expensive hand held marine 12V spotlights over the years but this light beats them hands down. It also has a red and a white camp light on the sides.
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Old 12-02-2021, 23:35   #11
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Re: Recharging an alkaline battery pack

Thanks all.

I’ll persist with what I have, it works well and the electrons on this boat come free from the sun. Seems it will be a bit of trial and error.

When this battery pack dies I’ll put something better in its place. Probably a lithium RC pack or something similar.
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Old 13-02-2021, 03:26   #12
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Re: Recharging an alkaline battery pack

Matt

Wouldn't this do the job?





You might get a better price than this.

https://www.ebay.com/itm/New-AA-Alka...MAAOSwqCtd5jQB
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Old 13-02-2021, 20:21   #13
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Re: Recharging an alkaline battery pack

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Matt

Wouldn't this do the job?





You might get a better price than this.

https://www.ebay.com/itm/New-AA-Alka...MAAOSwqCtd5jQB


The problem is that I’d have to pull the battery pack out of the torch, then pull the pack apart.

I’m experimenting with direct USB charging. The charge current is trivial but it is in the correct direction and doesn’t look like it will set fire to anything.
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Old 13-02-2021, 21:08   #14
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Re: Recharging an alkaline battery pack

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Originally Posted by GILow View Post
The problem is that I’d have to pull the battery pack out of the torch, then pull the pack apart.

I’m experimenting with direct USB charging. The charge current is trivial but it is in the correct direction and doesn’t look like it will set fire to anything.

I see what you mean.

My Cree torch is just a single battery 4.2V. The battery can be removed but I just use a very small plug in charger something like this (below)

What you are planning sounds good. I'm not happy about leaving any of these very cheap battery chargers on charge unsupervised so, like you, I'd initially use it outside just to check it out.

https://www.ebay.com.au/itm/DC-4-2v-...-/173655409818
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