How To Connect Two Batteries In Parallel Method, Safety And Mismatching

The main concept, when you are connecting two batteries in parallel, is that you are adding the amp hour ratings of both batteries, keeping the voltage same. For example, if you connect two 6 volt 4.5 Ah batteries in parallel, they are capable of providing 6 volt 9 Ah(4.5 Ah + 4.5 Ah) and in the case of four 1.2 volt 2,000 mAh wired in parallel connection, they can provide 1.2 volt 8,000 mAh (2,000 mAh x 4). If you want to connect two batteries of dissimilar voltages in parallel, there is a very big no for this process. The battery containing higher voltage will charge the battery containing lower voltage for creating a balance in the circuit. The reason for not recommending this process is that primary (disposable) batteries are not designed in a way to take the charge and so the battery with lower voltage will overheat and due to this it may leak or bulge. For extreme circumstances where the voltages are not similar, the primary battery may explode and in case of secondary (rechargeable) batteries, the lower voltage battery can not charge above a certain limit, but the higher voltage battery will still try. As a result, over heating, leaking or bulging may occur in the lower or higher voltage battery as it drains immediately. The larger the difference in voltage the greater are the chances of battery explosion.

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If you mix batteries’ companies even of the same voltage, you can face problems. Because of the unlike manufacturing processes, the voltages of batteries from distinctive producers may vary slightly. It means a 1.5 volt battery from company P could exactly be 1.6 volts, while a 1.5 volt battery from company R could be 1.55 volts. If these batteries are connected in parallel, you can experience problems other than explosion because for primary batteries, the stronger battery will anyway try to charge the weaker one and reduce the lifespan of both batteries and for secondary batteries ,the stronger battery will charge the weaker one, drain itself and waste energy.

In case if you connect rechargeable batteries in parallel and one of them is discharged while the others are charged, the charged batteries will try to charge the discharged one. The charged batteries will overheat as they immediately drain and the discharged unit will overheat as it starts to charge above its design capacities.

If you connect batteries of different ages, the batteries that are older will always have a lower voltage as all batteries self-discharge with the passage of time and even rechargeable batteries will not recharge to the same level like new batteries. To prevent the chances of any problem, you should follow some safety guidelines when connecting. In case of primary batteries, only use batteries with the same company and age. Also double check the voltages of each battery with the help of a voltmeter. For secondary batteries use batteries of similar company and age and before connecting make sure all the units are fully charged. If you are uncertain about this, connect them individually to a charger or check the voltage with a voltmeter.

It is possible to Connect batteries with different amp hour capacities in parallel and this won’t cause any major problems, but it is important to consider some potential problems like checking your battery chemistries because Sealed Lead Acid batteries have different charge limits than flooded lead acid batteries. It means if you recharge two batteries together, some batteries will never charge fully. As a result, there would be sulfation of those that never charge fully, reducing their lifespan. Double check voltages, if you are connecting batteries with unlike amp hour capacities, it is likely that the voltages will be dissimilar (even if the voltage on the labels are same). Also check it with a voltmeter otherwise you will experience issues .

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How to connect two batteries in parallel to the inverter?

You can connect many batteries in parallel with your power inverter or solar hybrid inverter for increasing its backup capacity. If you have a single battery inverter, you can connect more batteries in parallel as the entire voltage of the system will remain constant while capacity multiplies. For connecting two batteries in parallel to the inverter, you have to make sure that your power inverter can at the same time afford charging multiple parallel connecting batteries. If the charger is not fast, you should not connect larger batteries. Also, check the inverter or UPS specifications to see if charging current could be accelerated as it will help your battery charging to boost and shorten the time period to fully charge batteries.

Is wiring batteries in parallel dangerous?

When two batteries are connected in a parallel circuit, the voltage remains constant, but the current is accelerated. This can be very beneficial in case of some devices. But  if the batteries are sensitive and they do not have any circuit for protection, then it can be very disastrous for both of the batteries

Is it safe to connect mismatched batteries in parallel?

It is strongly discouraged to connect batteries in parallel applications, if the batteries are mismatched in age, size and type. Different companies of batteries can have distinctive charging and discharging properties, like accepting a charge or delivering current fast. It can also be possible even if the batteries are the same size. Different batteries (flooded or AGM) also can have distinctive charge/discharge properties. If you try to connect two or more batteries that do not charge and discharge at a similar rate, one battery will end up overcharged while the other one will end up undercharged. That is why this process is not recommended as you don't want to create  any problem with your batteries, as it can shorten the lifespan of both batteries and could potentially create a dangerous situation, if one battery gets overcharged.

Conclusion

If you are connecting batteries in parallel, the very important thing to consider is that batteries have similar size, chemical construction, voltage and capacity. The batteries connected in parallel having all of these things the same, will provide power to the circuit rapidly and efficiently. And if these factors are ignored, especially the same voltage and capacity of the battery, it can be dangerous for both the batteries.