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Home / SLA Battery Charger / How to Charge SLA Batteries

Charging Batteries and Battery Packs

Properly charging and maintaining your sealed lead acid battery is essential for a long battery life. With many different lead acid battery chargers, it is easy to find one that fits your needs. Here you will find how to connect a charger and battery. Note: sulfuric acid contained in the battery is extremely corrosive. Protect yourself with safety gloves and glasses when handling SLA batteries.

Connecting One Battery and One Charger


Figure 1.

This is the most basic connection of a battery and a lead acid battery charger. Make sure you ALWAYS connect the charger and the battery correctly. From the charger's positive (red) output connector to the positive battery terminal. The charger's (black) output connector connects to the negative battery terminals.
Remember: connect positive to positive and negative to negative. The charger and battery must have the same voltage

Charging Batteries in Series Configuration

It is possible for one charger to charge multiple batteries at once. These examples are listed for your reference only. If you do not completely understand these examples or how to connect the charger, we recommend contacting an experienced technician. Connecting the charger incorrectly can cause the battery to expand, and will consequently damage the battery and/or charger.

Connecting Two Batteries in Series, and Two Chargers


Figure 2.

In the example above, it shows two 12V batteries connected in series; resulting in a 24 volt battery pack. Connecting each battery to an individual battery charger is probably the best way to ensure each battery is completely recharged to full capacity. Using two chargers eliminates most of the problems associated with cycling batteries in series.

Connecting Two Batteries in Series, One Charger


Figure 3.

24V battery packs can also be recharged using a single 24 volt battery charger.

Charger Batteries in Parallel Configuration


Figure 4.
In the figure 4, we have paired two 12 volt batteries in a parallel connection. A parallel connection is where the voltage remains the same and the amp-hour increases. It can be recharged using a single 12V charger. Note the blue wire (W1), the purpose of this wire is to balance the voltage drop evenly across both batteries and each wire during charging.This isn't critical for lower current chargers, but when you start using chargers in the 10 amp and up range, the voltage differential can be significant. The blue wire (W1) must be connected to the opposite end of the battery pack as the red wire at the top of the battery pack.

Charging Batteries in Series / Parallel

Charging Four batteries in Series/Parallel (Example 1)
Figure 5.

In Figure 5, this is method is the best way to charge batteries connected in a series/parallel configuration. A single 24 volt sealed lead acid charger will do a better job than using two 12V chargers. Just like in figure 4, wire W1 is used to balance the voltage drop evenly across both batteries and each wire during charging. Two Chargers, Four Batteries Series/Parallel (example 2)
Figure 6.

Figure 6 we have two sets of two batteries connected in parallel. Then those two parallel sets are connected in series by a singer wire (W3). You can use a single 24V charger, like in figure 5, without having to worry about voltage imbalance.