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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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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 Jan 30 at 23:06
  • 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. – Aloysius Defenestrate Jan 31 at 4:30
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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 Jan 30 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 Jan 30 at 16:34

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