will adding another battery to my smartwatch double its battery life?

[Legolessed]

41 minutes ago, KaminKevCrew said:

Since it's a parallel circuit, that shouldn't actually matter at all. You can add as many batteries as you want, and they'll all draw down to the end voltage at about the same time. 

Yes, that's a parallel circuit.

Balanced charging is where you charge the battery cells individually, rather than both at once. It's a very important thing to do with Li batteries. 

 

To give you an example, if one battery were at, say 3.2V and the other were at 4.0V, but you're charging both at the same time, you would end up blowing up the battery that's at 4V because you would be attempting to over charge it. balanced charging means that you charge each cell to the appropriate voltage individually, to avoid that.

 

You should read this: http://www.instructables.com/id/Lithium-Polymer-Etiquette/step5/Balance-Charging-Setup/

https://www.homepower.com/articles/solar-electricity/design-installation/ask-experts-batteries-series-parallel

 

this says that you can charge the batteries over one source as long as its in parallel not series 

[KaminKevCrew]

22 minutes ago, Legolessed said:

is there any way to do it without one of those?

no.

[Legolessed]

4 minutes ago, KaminKevCrew said:

no.

https://www.homepower.com/articles/solar-electricity/design-installation/ask-experts-batteries-series-parallel

 

[KaminKevCrew]

3 hours ago, Legolessed said:

https://www.homepower.com/articles/solar-electricity/design-installation/ask-experts-batteries-series-parallel

 

Okay, what about it?

[Legolessed]

15 hours ago, KaminKevCrew said:

Okay, what about it?

its says in parallel that the batteries are fine being different sizes and being charged off one power source 

[Unimportant]

If you connect the batteries in parallel the voltage will stay the same, the device will work fine and the battery life will indeed be increased. Balancing is only required for charing Li-ions in series, not parallel.

 

The possible problem is charging. The charging circuit is designed for the original 240mAh battery, it might not be able to charge the 2 batteries (or a single larger battery, which is essentially the same). You'd have to test.