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Can I Connect Two Batteries of Different Voltage in Parallel? 

 September 19, 2021

By  Phil Borges

Connecting batteries in parallel is a way to generate output. However, there are several considerations that are important to keep in mind here, including what happens when you try to connect two batteries of different voltages in parallel.

You should not connect two batteries of different voltages in parallel as the one with the higher voltage will try to create a balanced voltage by discharging the one with the lower voltage. This could then end up causing the batteries to fail.

There are a few other things to consider in this case such as the brand, recharging, age of the battery and more, which can also affect your batteries. Read ahead to find out more.

Can Batteries of Different Capacity in Parallel?

You should not connect batteries of different capacities in parallel as this could end up damaging them. The battery with a higher capacity will try to even out the voltage by reducing the charge of the battery with a lower capacity.

If the difference in voltage between the two batteries is minor, the current will pass from the higher to lower voltage, leading to overheating and stopping the flow of the current.

On the other hand, if the voltage difference is significant, then the current flow can cause the battery to leak, discharge or even explode completely, leading to a hazardous situation.

The impact of this kind of situation depends on the kind of battery as well. For instance, if the batteries are disposable, they could overheat, leak or explode.

If they are rechargeable, the impact might be lesser since the battery with a lower capacity will stop accepting a charge beyond a certain extent even though the current will keep flowing.

Can You Connect Batteries in Parallel from Different Brands?

Ideally, you should not connect batteries in parallel from different brands, even if they claim to have the same voltage. This is because different brands resort to different ways when it comes to producing these batteries.

Due to this difference, there is always bound to be a minor difference in the voltages of the two batteries, causing the current to flow from a higher to a lower voltage.

While this might not cause significant damage, like leakages or explosions, it might still cause the battery to overheat, leading to minor damage in terms of how long the battery can function efficiently.

This kind of effect could occur even if the voltage difference is as minor as 0.5 volts.

Can You Connect Discharged and Charged Batteries in Parallel?

You cannot connect discharged and charged batteries in parallel. With a higher voltage capacity, the current will flow from the charged to the discharged battery in order to bring the batteries to a balance.

However, instead of creating a balance, both the charged and discharged batteries will only end up taking more heat than they can handle, causing them to leak or explode.

Can You Connect New and Old Batteries?

Connecting new and old batteries will not be efficient. Since batteries tend to lose charge as time passes, the old batteries will be the ones with the reduced capacity and the inability to create a balance with the new battery.

While the consequent impact of connecting new and old batteries in parallel might not be extreme, it could still lead to a much lower output than required for your device.

Additionally, the newer battery’s lifespan will reduce quicker as well when combined with the older battery.

Things to Consider

It is now clear that you need to keep in mind certain things that could ensure a balance between the batteries when they are connected in parallel. Let’s take a look at what these are.

The batteries should belong to a single brand so that you can maintain and match the voltage between both batteries.

They should have the same manufacturing and expiry date such that neither of them has lost any charge.

Both the batteries should carry the same amount of charge so that there are no issues once you connect them together in parallel.

You should ensure that you connect the batteries to their respective terminals so that they can work well.

In case you have any further doubts about connecting the two batteries, you can refer to user manuals to get a basic idea about the process and precautions.

Frequently Asked Questions

Can you connect batteries in parallel with different amp hours?

Yes, even if the batteries you’re trying to connect have different amp hours, you can still connect them. This is unlikely to cause any problems with the batteries and will continue to provide efficiency.

However, even in this case, you should ensure that the voltage of both batteries is the same as this could otherwise lead to issues like overheating, leakage or explosions.

To maintain this voltage level, you will also have to maintain the brand and age.

In this case, an additional factor that could affect the efficiency is the material and composition of the batteries. As long as they are of the same composition, you will be able to connect them in parallel even with different amp hours.

Can I mix batteries with different mAh?

You should not mix batteries with different mAh (milliamp hour) as this could result in one battery having a higher capacity than the other one, causing a lack of balance and fluctuation in terms of the current.

This can further lead to the batteries losing out on their cells and capacities at different rates, leading to a range of issues like overheating or over-discharging.

The impact can be differently felt if you connect them in series or in parallel, but it is likely to reduce the lifespan of both batteries.

What is the right way to connect batteries in parallel?

In order to connect two batteries in parallel, you must maintain the same voltage while trying to increase the amp-hour capacity. To do this, you should use a jumper cable to attach the positive terminals of each battery as well as the negative terminals with each other.

Is there a difference between connecting batteries in parallel and in series?

Connecting a battery in parallel maintains a constant voltage throughout while altering the amp hours.

On the other hand, connecting batteries in series includes maintaining the same amp hours while altering the voltage.

For connecting in parallel, the positive terminals are connected with each other and the same goes for the negative terminals. However, connecting batteries in series involves connecting the negative terminal of one battery with the positive terminal of the other battery through a jumper cable.

It is also possible to create a simultaneous in series and in parallel connection by simply connecting the negative and positive terminals of two different parallel connections.

What uses do batteries connected in parallel serve?

If you connect two batteries in parallel provided that the voltage remains the same, you can use these for a range of functions such as powering cells and batteries of multiple devices.

A parallel circuit can be advantageous as it can supply power across multiple devices without reducing the voltage. Even if one connected device stops working, the others will continue to function.

Will I have to replace the damaged battery?

In case you end up using two batteries of different voltages in parallel, you will not only have to replace the battery with the lower voltage but also the one with the higher voltage.

This is because both of them will end up overheating, perhaps even leading them to leak or explode. To maintain safety and prevent further damage, it is important for you to replace both batteries so that the new ones have the same voltage level in parallel.

Can overheated batteries damage the appliance or device?

If you do not immediately remove the overheated batteries in parallel from the device or connection, they could definitely end up causing damage to the appliance or device that they were meant to power.

This is because leakages or sparks can end up burning parts of the appliance as well while also releasing harmful gases that could prevent the device from performing well.

About the author

Hi, I'm Phil Borges.. thanks for reading.. My wife says I can't shut up about batteries so to save my marriage I've started this blog .. where I'd be ranting about batteries! Please leave a comment if you have any questions, I'm happy to help!

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