Mixing batteries - safe?

Okay, I have a question about mixing batteries of different voltages. Is it okay to pair a 3.7v with a 1.5v battery in series? I tried this on one of my 'cheaper' pointers to see if it would work and low and behold it did... I figured I'd either damage the driver or kill the diode by doing that but the laser worked perfectly fine. I checked the voltage of the two batteries together and they were outputting ~5.5v together so it was still in range of the flexdrive. Are there any dangers of running a battery configuration like this? The only reason I did it was because I didn't have a AAA sized spacer.

This is a very good question to ask as I'm sure there has been lots of people wondering about it esp since you see so much printed about not mixing cell types.
You can do this, no problem for the diode for sure and most likely none for the driver either, the only prob I see is for one of the cells, at some point one will be dead or even ruined.
Let us know which dies first, my guess is the 1.5 since it is the lower voltage. I wouldn't be a bit supprised if the buck boost driver didn't suck the 1.5 volt cell into reverse polarity once it reaches 0 volts

I'll keep monitoring it to see what happens... just for record keeping the 3.7v is a SoShine Lithium-ion rechargeable and the 1.5v is an Energizer lithium.

Flaminpyro said:

Let us know which dies first, my guess is the 1.5 since it is the lower voltage. I wouldn't be a bit supprised if the buck boost driver didn't suck the 1.5 volt cell into reverse polarity once it reaches 0 volts

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To the original question, as long as both batteries can provide the required current, then there's no issue while they remain charged. I think that the one with the lower Ah capacity will die first, and they'd supply energy in the approx ratio of 3:1 (li-ion vs other), but the voltage across the other cell won't go negative - though I don't in all honesty know what *would* happen, either - I suspect the battery with the larger capacity pushes current through the other battery which essentially becomes a resistor (battery internal resistance) and current/voltage input to the circuit drops. Electronics gurus, feel free to enlighten us, though - that's only a guess.

In general, people recommend against mixing batteries. I cannot say myself, I haven't researched evidence or seen first hand what happens, but I have heard stories of people using mismatched batteries (same chemistry, different voltages) and having a "catastrophic failure," I.E. the battery tube ruptured after the cells vented with flame. In this case, I think your 1.5V would be more at risk, and those generally don't explode... Just keep an eye on it.

As far as operation of the device, why mix two batteries anyways? Why not just use two Li-Ions and, say, a generic silicon diode in-line?

It's okay for a few minutes, but don't design around it. You WILL kill the lesser of the two eventually. Explosions are unlikely, and you may not care if the batteries in question are disposable. But lithiums aren't cheap enough to warrant this configuration.

Exactly. You can mix them for testing as long as you are and remain certain neither battery is empty.

As soon as one battery is empty, the still running current (from the good battery) will start to reverse-charge that battery resulting in certain death for that battery, but also potentially dangerous situations.

If they are equal size, the one with higher voltage is likely to be the one that dies: if the energy density is comparable, a cell with higher voltage will have fewer mAh's in the same package... and since they are in series, both cells are discharged with the same current.

ohhhh.... i think i get the picture now.

so like if one dies first and is left in series the 2nd battery would be like charging it. but with reverse polarity. ok... that totally makes sense on why to never mix different capacity batteries.

it'd be the same way as if you stuck the dead battery in a battery charger backwards.(positive pin on negative battery and negative on positive battery). basically that's what a battery charger is... a circuit that sends volts and current and when you place the battery it's in parallel circuit to the charger, but in the case of the different cells it's series so it charges it all wrong.

same idea like when you jump a car. you run parallel circuit.. positive to positive and negative to negative. but if you complete the circuit in series that can actually cause the battery to explode or other detrimental results.

damn... why didn't i think of that whole different capacity notion sooner? thanks for the question and other posts. makes so much sense now... if i understood it wrong then correct me XD

voltage doesnt matter but keep the larger voltage in the front so dont put 9 into a 1.5 and you will be fine without question

+-+- =series so the voltage adds
+- connecting the two positive ends to the circuit= parallel
+-

you will be fine just dont mix like alkaline and lithium or anything

you shouldnt have troubles doing 1.5v <-- 9v but i wouldnt suggest it

MikeBP said:

voltage doesnt matter but keep the larger voltage in the front so dont put 9 into a 1.5 and you will be fine without question
+-+- =series so the voltage adds
+- connecting the two positive ends to the circuit= parallel
+-
you will be fine just dont mix like alkaline and lithium or anything

you shouldnt have troubles doing 1.5v <-- 9v but i wouldnt suggest it

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Do you intentionally try to be confusing? :thinking:

It should be OK, but don't do it :wtf:

How do you put those two ideas together? :tsk:

Peace,
dave

Consider it, you can go bridge jumping but i wouldnt suggest it, it potentially can be harmful if done incorrectly so i dont suggest it.



<--- she is so fuckin hot... I love my avatar

MikeBP said:

Consider it, you can go bridge jumping but i wouldnt suggest it, it potentially can be harmful if done incorrectly so i dont suggest it.

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So it is intentional. You try to make yourself sound smarter by being intentionally obtuse

Your argument is what is known as an invalid analogy.

Even the statement above which you used to "explain" your earlier statement is internally inconsistent.

You remind me of The Sphinx from Mystery Men

You just became a person of interest

Peace,
dave

O crap this is going to be fun op:

Flaminpyro said:

O crap this is going to be fun op:

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No kiddin, Mike already has 6 red bars, there are even light colored red bars, which we did not know until now
I really did not thought that someone could actually get into such negative reputation, and stick around. And still not doing anything specific to get better.

And the comment about the avatar.

Group facepalm anyone?

Eudaimonium said:

Group facepalm anyone?

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"Group facepalm" ? ..... what's, that, a group buy for facepalms ? ..... (LOL )

Seriously, NO, never mix batteries, except if you're searching troubles intentionally.

You can end with dead batteries, acid leakage, or even exploding cells (mostly in Li-Ion unprotected cells, but also sealed alkaline can explode in certain conditions)

Normally, when is matter of rechargeable batteries, is also a thing to avoid, to just mix identical batteries with different charge levels, like, if you have an apparate with 2 different sets of batteries, never mix the batteries from different sets ..... as example, mixing a full charged battery with low charged ones in the charger, the full charged one go in overcharge and explode ..... same, mixing a low charged battery with a full charged set in an apparate, the low charged one go in undercharge or also in reversal flow, and die or leak acid or burn ..... or in case of protected cells, it don't die but the apparate stop to work and you don't know why .....

Is alway good use is to mark the different sets of rechargeable with different colors or writes, and never mix them .....

Only if you're using primary batteries and don't care about them, e.g. you use them for an emergency use or for a test, and then throw them away, you can risk to mix them ..... still a not good thing to do, but acceptable, in these cases ..... not for normal use.

HIMNL9 said:

"Group facepalm" ? ..... what's, that, a group buy for facepalms ? ..... (LOL )

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Think: Naked Gun III theater
That was a good group facepalm

Negative of 625 reputation point sure deserves a group facepalm, on top of all, comment about the avatar.