You can connect batteries in series or parallel. Each option has a separate set of benefits and weaknesses:
The biggest difference between series and parallel connections is the objective. You connect batteries in series to increase the voltage. For instance, combining a 12V battery with another 12V battery in series gives you 24 volts.
But this only works if you have the same voltage. For instance, you can’t pair 6V and 12V batteries in series. Doing so may destroy the batteries involved.
If the voltage matches, you can connect multiple batteries in series by running a line from one battery’s negative terminal to another battery’s positive terminal. If you succeed, make sure the charger’s rating matches the voltage of the new battery system.
Consumers want to know whether you can connect different amp-hour batteries in parallel because a parallel connection increases the amp-hours. For instance, merging two 12V 100Ah batteries in parallel will produce a 12V 200Ah system.
In this case, you connect one battery’s negative terminal to another battery’s negative terminal and the positive terminal to the positive terminal.
Parallel VS Series
- You connect batteries in series when you want to accommodate large applications. The high voltage reduces the system current, which, in turn, allows you to apply thinner conductors without making the voltage drop worse.
- Connecting batteries in series prevents you from connecting the resulting battery system to devices with a lower voltage. For instance, if you combine two 12V batteries, you can’t use the resulting 24V battery system to run a 12V appliance. This is not a problem when you connect batteries in parallel because the voltage stays the same.
- Parallel connections allow your applications to run for longer periods because the amp hours have increased.
- A defect in one battery in a parallel connection doesn’t affect the other batteries.
- Batteries in parallel systems take longer to charge because of the elevated capacity.
- Both options are equally safe. You can’t argue that parallel is safer than series or vice versa. Things will only go wrong if you mix battery types and voltages.
- Technically, neither option is better than the other. The application will determine your selection. You may even settle for a third option: series-parallel. First, you connect two sets of batteries in series. And then, you create a parallel connection from one battery set to the other.
- Series-parallel does not mean wiring batteries in series and parallel simultaneously. This configuration would lead to a short.
What Happens When You Mix Different Amp Hour Batteries In Parallel?
Experts emphasize the dangers of mixing different voltages in parallel because the practice is more dangerous. The consequences are significant. The higher voltage battery will funnel its current into the lower voltage battery in an effort to charge it. This is bad if you have a non-rechargeable battery because it will overheat, leak, bulge, and possibly even explode.
If you have a rechargeable battery, the consequences are the same. The higher voltage battery will attempt to charge the lower voltage battery.
Overheating, leaking, and bulging can still occur, not to mention fires and explosions, but they are not guaranteed. In fact, you may only encounter trouble if your battery is incapable of charging above a specific point. Otherwise, if you’re lucky, nothing will happen.
People rarely concern themselves with batteries with different amp hours because nothing significant will happen if you connect them in parallel. The principle you encounter in batteries with different voltages applies here.
The batteries will attempt to find an equilibrium. Take two containers of water as an example. If container A has more water than container B, running a hose from the bottom of container A to container B will compel the water to flow from A to B until their water levels equalize. Expect something similar to happen in batteries with different amp hours.
I discourage this practice because the lower-capacity battery will charge faster. Therefore, you risk overcharging it. Secondly, the higher-capacity battery may monopolize the battery charger, causing the smaller battery to charge at a slower rate.
Additionally, the batteries won’t deplete evenly. All in all, connecting batteries with different amp hours in parallel is permissible if you have the same battery types and voltages. Technically speaking, nothing bad will happen.
The consequences mentioned above are the worst-case scenarios. However, it is safer to use the same amp hours.
How To Connect Different Amp Hour Battery In Parallel?
- Connect one battery’s negative terminal to another battery’s negative terminals.
- Connect the positive terminals together.
- Run a line between the last battery’s positive terminal and the application.
- Repeat this final step for the negative terminal.
You should keep the following in mind:
1). User batteries with a lower voltage and higher capacities. This minimizes the number of parallel wires.
2). Use the same battery type. For instance, avoid pairing sealed lead acid and flooded lead acid batteries because they have different charge points. You can’t guarantee that every battery will attain a full charge. Sulfation will afflict the batteries that can’t charge fully.
3). Make sure the voltage is the same. Don’t make assumptions. Test the batteries with a voltmeter to confirm the voltage. In many cases, the voltage changes in batteries with different amp hours.
This is why some experts warn against mixing brands. Some brands have slightly different voltages and amp hours. For instance, some brands may label their batteries with a 1.5V rating when the actual voltage is 1.6.
3). If you have lithium batteries, charge them separately before connecting the batteries in parallel. This eliminates the challenges mentioned above where the higher-capacity battery attempts to charge the lower-capacity battery.
4). Don’t forget to upgrade the wiring. Keep in mind that connecting batteries in parallel increases the amp hours. In other words, you need a line capable of withstanding the elevated current.
Pay attention to the length. A longer cable increases the battery pack’s resistance, which makes overheating, fires, and explosions more likely.
5). Don’t reverse the polarity. Make sure the positive terminals are connected to one another. The same goes for the negative terminals. Otherwise, you may accidentally connect the batteries in parallel and in series.
6). Even though a battery system connected in parallel can still provide power when one battery fails, you can respond to a defect in one battery by replacing all the batteries. This assumes that you have lithium batteries.
What Amp Hour Battery Is Best To Connect In Parallel?
No one amp-hour is more conducive for a parallel connection than another. The only important consideration is to match the amp hours. You can get away with connecting different amp-hour batteries in parallel, but the practice has drawbacks. Keep the following in mind:
- Batteries with different capacities are annoying because the lower-capacity battery will deplete faster.
- If you can’t find batteries with the same capacities, make sure the difference in amp hours is as small as possible.
- Try to match the age. At the very least, you shouldn’t mix new batteries with their older counterparts. The old batteries will become a burden to the new ones.
- Connecting cells in parallel directly and permanently is okay because the stronger cells can help the weaker ones.
- Don’t connect a full cell to an empty one. This can happen with batteries in cell holders. Anyone can replace a full cell with an empty one.
- Batteries whose balance connectors are not directly paralleled are problematic because you need to give each battery a BMS to plug into the balance connector. Having the balance connectors directly paralleled can cause an inrush of current through the balance connector, melting the wires.
Ultimately, the safest option is to connect the cells in parallel directly and permanently. Otherwise, find one battery on the market with a capacity large enough to accommodate the application you want to power.
While mixing amp hours is not inherently dangerous, you don’t want to take chances. It only takes one wiring mistake for a battery to explode.