# Practical usage of batteries connected in parallel

Is there any practical usage in real devices for connecting batteries in parallel? Or is it more a theoretical construct? It seems to me that only batteries in series are used nowdays.

• I have two appliances in my home that use batteries connected in parallel; One is an alarm clock, and the other is a camping lantern. The alarm clock has spaces for two AA cells, but it will run with just a single cell in either space. The alarm is a motor that rings a physical bell. That uses significant battery juice. It will run longer if you insert two batteries. The camping lantern will run on either four or eight D cells (i.e., either one or two strings of four series cells each). Same deal: It'll run twice as long if you fill all eight slots instead of filling just four of them. – Solomon Slow Mar 4 '19 at 20:28

Of course there is. If you want to ramp up the current from a battery source without increasing the voltage, you connect your batteries in parallel. A series connection increases the voltage but the current stays constant. Just basic Kirchoff's law.

Batteries placed in series have a higher voltage that is the voltages are summed. Batteries placed in parallel can withstand a higher load. Thus engineers match series parallel configurations to meet voltage and load requirements for everything from the 9 volt in your smoke detector to multi kilowatt uninterruptable power supplies.

The first consideration is the voltage requirements for the load. Some loads (motors in particular) won't run at all unless there is sufficient voltage.

The next consideration is the demand (magnitude of the load) on the battery. There are two aspects of demand- how much current the load needs to operate and how much energy the load will consume (power x time) for the expected duration of the load.

Connecting identical batteries in series increases the voltage, but not the current delivering capacity of the batteries. Connecting batteries in parallel increases the current available from the batteries, but not the voltage.

If you simply need more voltage, you can connect the batteries in series.

If you need more current but not more voltage (over voltage can damage some loads) you can do several things. You can connect identical batteries in parallel. Or you can use a bigger battery, e.g., replace a AAA battery with a AA battery (both 1.5 volts for alkaline), or replace a C battery with a D battery, in all cases space permitting. The same applies if you need more stored energy (power x time), but not more voltage.

Finally, the reason you don't see too many batteries in parallel is because unless the voltages are perfectly matched, one battery may attempt to charge the other causing damage in the case of a non rechargeable battery.. Instead, you use a bigger single battery (e.g., replace a AAA with a AA).

Hope this helps.

• So, different voltages make one battery charge another one? If not chargeable, just heat up? What is the flow of electrons in parallel schema? thanks! – Pavel Mar 5 '19 at 8:18
• I didn’t mean “charge” literally. I meant one battery might attempt to charge the other, which for a non rechargeable battery could be dangerous – Bob D Mar 5 '19 at 8:59
• Or destructive. See edit – Bob D Mar 5 '19 at 9:07