So I have this rechargeable fan with a 3,700mAh 3.7v battery (pictures attached). If I added another battery 3.7v battery to this circuit board, will it damage it? I also learned that parallel and series connection will give different results, voltage/current. What type of connection should apply? I just want the battery to last longer.

 

If I added another battery 3.7v battery to this circuit board, will it damage it?

Maybe, maybe not. It depends partially on whether the charging circuit can handle the additional capacity.

I also learned that parallel and series connection will give different results, voltage/current. What type of connection should apply?

The device is intended to operate at 3.7V, so you'd obviously need a parallel connection. But, the devil is in the details. To parallel the batteries, they should be matched for best performance.

I just want the battery to last longer.

The battery pack already has 3 cells in parallel. You could just about double the capacity by using one with cells in the 2-3Ah range. That is if the charging circuitry can handle the extra capacity.

Be aware that any 18650 cells advertising more than 2-3Ah capacity are likely fakes. If the cells are 18500, that's about the maximum Ah capacity. I think legitimate cells are in the 1.6-1.8Ah range.

 

Adding a battery in series is a no-no. That would double the voltage.

You could possibly add another (identical) battery in parallel. If you do that the voltages MUST be the same when you do so. And it •might• work. By work, I mean it will last twice as long. But it will also take twice as long to charge. That is, if the charging circuit works correctly, i.e. still provides the same current. If it does not, it might well be damaged.

Your call. It might work or might be damaged.

 

Maybe, maybe not

You beat me to it! At least we said same thing.

 

Did the battery pack give adequate run time and no longer does? I'd be tempted to simply replace it with another similar pack. Good quality 18650 cells are a LOT better than cheap, lousy ones.

 

Parallel is correct.
The fan will have a longer run time.

This can be graphed by using a multimeter measuring the current over time.
An CFM is a concideration, the rpm slows as the voltage drops.
It is likely the engineer chose a milliamp draw, that is the fan motor to match the voltage range of a cost effective battery pak.
The operating performance of the fan and the targeted market in sales.
Going further with higher cost, a high efficiency DC - DC converter and a high efficiency fan to another targeted market.

We measure the mA draw and run time. We can extend the run time by using a higher mA/Hr rating.
Calculator example fan drawing 100mA. 0.1A.... 2000mA Hr 2AH notice the % efficiency
https://batteryzone.org/battery-runtime-calculator/


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The correct way is to remove the battery that is already there.
Replace that battery with another battery of the same voltage but higher mAh number, for example, 3.7 V, 5200 mAh.

 

The correct way is to remove the battery that is already there.
Replace that battery with another battery of the same voltage but higher mAh number, for example, 3.7 V, 5200 mAh.

I will try this instead.

 

Maybe, maybe not. It depends partially on whether the charging circuit can handle the additional capacity.
The device is intended to operate at 3.7V, so you'd obviously need a parallel connection. But, the devil is in the details. To parallel the batteries, they should be matched for best performance.
The battery pack already has 3 cells in parallel. You could just about double the capacity by using one with cells in the 2-3Ah range. That is if the charging circuitry can handle the extra capacity.

Be aware that any 18650 cells advertising more than 2-3Ah capacity are likely fakes. If the cells are 18500, that's about the maximum Ah capacity. I think legitimate cells are in the 1.6-1.8Ah range.

Thank you for your amazing support. I never knew that there is something called charging circuitry that can get damaged if not designs to handle extra capacity. I will just replace the battery with a similar 3.7v but higher mah capacity. I hope this works.

 

Thank you for your amazing support. I never knew that there is something called charging circuitry that can get damaged if not designs to handle extra capacity. I will just replace the battery with a similar 3.7v but higher mah capacity. I hope this works.

That depends in the charging circuitry. Switching to a higher capacity battery might be problematic as well. There is actually no difference between adding an identical battery in parallel and substituting one with twice the capacity.

I actually think it is unlikely to damage anything either way, more likely it will just take twice as long to charge.

 

I will just replace the battery with a similar 3.7v but higher mah capacity. I hope this works.

The problem remains. Best case, the higher capacity battery will just take longer to charge. Worst case, something gets damaged.