Battery Chargers:

A battery charger is a device that stops the flow of electricity in a lead-acid or gel cell battery when it has reached full charge. They are often found in cars, trucks, boats, and recreational watercraft.

How They Work:

A battery charger usually consists of three components: a capacitor or battery-theory cell, a voltage regulator, and an ammeter. The capacitor and the ammeter serve as protection against overcharging and overloading, respectively. The regulator reduces the input voltage to a level appropriate for charging. The charger couples with the battery terminals to charge the battery.

Charging Speed:

Charging speeds differ based on the battery’s type, charging voltage, charging current, and charging time. The rate of charge is impacted by the difference between T1 and T2 times. Therefore, to charge a 1-hour lead-acid battery at 12 volts at 1 amp for an hour requires 1 hr sufficient time.

Adding Two Battery Chargers in Parallel to Speed up My Charging Time:

You can add two battery chargers of the same rating in parallel to speed up charging time. This is because the charger has a constant voltage and current, but one has 1 amp and another two amps and a different voltage (2 V vs. 1 V). The combined power will make up the desired charge rate of 2 amp each with higher voltages for more power. Charging times vary depending on many different factors, including the type of charger being used, the size and type of battery being charged, and how deeply discharged it is.

Now, both chargers together will charge faster than just one can do alone. If you charge at 1 amp for 1 hour and then two amps the next hour, the total charge time would be 3 hours. Adding two more chargers will reduce that to two hours. So your battery will not only be charged faster but also safer, as occasional overcharge can damage batteries and shorten their life.

Overcharging Battery:

Be careful not to damage your battery or charger by overcharging. Charging time depends on the battery’s capacity but can be estimated by dividing its capacity in mAh by its charge rate: 5 hours for an 1800 mAh cell at 1 amp and 3 hours for a 2200 mAh version at two amps. For example, in our example, we alternate their use every hour: 1 hour at 1 amp and another hour at two amps will take 3 hours.

If you will ever use more than one charger for one battery, it is best to use some battery management system, which can automatically balance the charge rate between the chargers.

Connecting Two Chargers in Parallel:

1) Connect the output of one charger to the input of another. You can do this with a regular power cord or by using a balun. A balun is an item that allows two different gauges of wire to be connected closely together without causing a voltage drop. Chargers usually have a small plug that will fit into the other end of a regular AC power cord, but not always, so you may have to use a regular AC power cord with an adapter.

2) Connect a small wire from one charger’s positive terminal to the other charger’s negative terminal. You can do this by removing a small screw from the side of one charger and connecting it with a wire to the other charger. Then reinsert the screw. This way, they will always be in parallel until you separate them. You can also add a switch or remove them from parallel, but this is an advanced topic and not covered in this article.

3) Use an AC power switch or an adapter that fits into both ends to turn off both chargers simultaneously, then turn on one of them when you want it. This saves another connection on either end.

Parallel Charging With the Wrong Rating:

Nothing, except that it would take longer to charge. This is because the higher-powered charger will waste power when it charges at 1 amp. One wastes 2/3 of its maximum power while the other wastes only one-third of its maximum power, but you cannot combine the two chargers in parallel with different ratings for most chargers. The reason is that if one charger can deliver two amps and the other 1 amp, power will be wasted in the 2-amp scenario. If there are two chargers at the same rating, they can be put in parallel.

Other than when purchasing, they are compatible. They will not waste power when in parallel. Thus, it can be used to charge several batteries of different mAh ratings simultaneously with only one charger.

You can combine them in series if their ratings are the same. For example, you could include two 1 amp NiCad/NiMh chargers in series using an adapter. Then connect this to your battery with a switch to turn it on, then turn on the other charger whenever you want it.

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Adding these two chargers in parallel will make charging faster. It is not recommended for charging most batteries, but most NiCad/NiMh batteries are good for this. This is especially true with 6-volt batteries, which can be combined in series. 


Q1: Why Can’t I Use Two of My 1 Amp Chargers at Once?

A: You can. They will work. It’s not recommended to charge most batteries, but it is safe and effective for most NiCad/NiMh batteries. 

Q2: What Will Happen if the Battery Is Overcharged?

A: It could be damaged. Overcharging also makes the battery-less useful and reduces its life over time. Try not to overcharge your battery by mistake! Battery condition is checked with a meter before charging, just like you would with a car battery, for example.

Q3: Can I Charge My High-Powered Batteries With Multiple Low Amp Chargers?

A: No, it is not recommended. They will work and charge fine, but your charging time will be longer. Even though the charger may show that it is charging, it may not be at full power, and you could accidentally overcharge your battery and damage it or reduce its life over time.