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I'm talking about something like this which allows you to use a Dewalt battery in a Makita tool.

Since this is just a question of connecting pins and so on, and no change of current or voltage is taking place, this should logically be ok as long as the battery is the same voltage as the one made by the same manufacturer as the tool, right?

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  • I bought one but it damaged the batteries (Makita) so as they wouldn't recharge. I would advise passing. Not a cheap fix. Commented Jun 25 at 6:09

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Logically, you're correct, but practically, you might run into problems.

For the purposes of this answer, I'm assuming you're only crossing lithium ion batteries from different manufacturers. (Crossing battery chemistries is even more fraught.)

Lithium ion batteries don't like being run down to an extremely low voltage. (This varies subtly by chemistry, so I'll suggest you look up your specifics. You're in the ballpark of 3.2v per cell, which will multiply out to whatever number of cells is in series in the battery.) If you run them "dry", they get damaged internally, and either won't recharge or might (in extreme cases) catch fire. You really don't want lithium ion fires in your life. (Google "Hydrogen fluoride".)

So power tool manufacturers have built a deliberate cutoff circuit in to prevent overdischarge and protect the battery. You'd have to know whether that cutoff circuitry is in the tool or the battery. Crossing manufacturers might leave you without a cutoff circuit. (And I frankly doubt that any cheap adapter has the smarts to have a cutoff, though I could be wrong.)

If you absolutely had to do this, you need to figure out what the cutoff voltage is for your particular battery and be sure that you don't overdischarge your battery. (You need a voltmeter of some description for this.) You also need to use the manufacturer's charger with their battery. (Even if the adapter works on the charger... just don't!)

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    Thanks. The two batteries are both lithium ion. Nevertheless I've decided not to go down this route of adapters. I'm not going to do it, but why would charging the battery using an adapter be particularly dangerous? I asked the seller of the adapter linked above and he also said that it couldn't be used for charging, but didn't explain why.
    – Ne Mo
    Commented Jan 30, 2020 at 23:06
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    Battery chargers are a whole another question, and I'd have to do a bunch of research to come up with a credible answer. The short version is that lithium ion batteries are usually charged with a CVCC method, but manufacturers will build in smarts, like temperature sensors, usually to optimize speed but also to prevent damage. Now that I think about it, I'm not sure a charger would even try to charge a 'foreign' battery. Commented Jan 31, 2020 at 4:30
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    Also Google "metal fire". Even without hazardous combustion products, you're talking about a reaction like magnesium or thermite, which is not something you can put out with mist home gire extinguishers (certainly not water). Worse, you're talking about that kind of reaction in a closed container; if it doesn't immediately melt sufficiently explosion is possible. The cost of packing that much energy into this small a container is that you really don't want to make guesses about compatibility.
    – keshlam
    Commented Jun 25 at 9:01
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    Beyond the two high-current terminals for actually running the tool (or for charging), many batteries also have a number of smaller pins. These might be used for such things as monitoring pack internal temperature or balancing charge across the cells in the pack. Cheap adapters don't connect these pins because they're cheap, but also manufacturer specific. A charger may refuse to operate when it sees these monitoring pins are disconnected.
    – Greg Hill
    Commented Jun 25 at 13:23
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No, it's a lot more complicated than that. An 18V pack might be NiCd, NiMH, Li-Ion, Li-Po or other technology. All of them charge and discharge differently, and the safety circuits may be different.

It's not a matter of "put only Apple brand accessories on your Mac"... it's a matter of electrical compatibility.

If your oh-so-clever adapter manages to put a lithium battery on a NiMH charger, you could have yourself a nice fire.

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A battery is container for power ( DC electricity ).

The only difference between the different manufacturers products is the connection interface that allows the DC current to be transferred from the battery to the tool. ( given that the two tools are of the same voltage I.E. a 20v dewalt vs a 20v craftsman )

The reason being they want your battery money to go to them and not to the competition.

In theory adapters should work ( i have not used any ) as long as the voltages are the same and they are of sufficient quality.

This a simplistic explanation, i am sure there are others more knowledgeable or verbose who may like to chime in. ( I am not a know-it-all, i just play one on the internet.)

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  • I agree as long as the voltage is the same there should be no problem I know several different adapters are out there, I haven’t used one as I have dewalt tools. Most batteries are made overseas from what I have seen the aftermarket batteries are seconds so there amp hours may not meet the pen standard but they work . +
    – Ed Beal
    Commented Jan 30, 2020 at 1:16
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    A battery is just a container for power, but a lithium ion battery pack has batteries and a controller that limits charging, current, and discharge level. So, things are more complicated now, but many manufacturers use similar setups, so I think there is still a high level of compatibility even tho no one will admit to it because lithium packs are very dangerous.
    – JPhi1618
    Commented Jan 30, 2020 at 16:34
  • In fact, this is one of the reasons high-power USB has become so popular; it simplifies the question of who is responsible for what. Unfortunately, tool manufacturers are now taking a large percentage of their profits from battery sales and have no interest in standardizing batteries and chargers across the industry.
    – keshlam
    Commented Jun 25 at 9:15

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