# Charging battery with constant voltage and current, with DC power supply

This question is for a general case. Is it possible to charge a battery (any voltage, any components) with constant voltage and current with a DC power supply. For example: charge a 12V 100Ah with 13.5 V constant, and 30A constant? It is for measurements and tests purpose. Is it still safe? Thank you very much :)

• Take a minute to search EE for this question, I'm very sure it have been answered already. Commented Oct 4, 2023 at 13:11
• Depends on chemistry. Lead-acid? Lithium-ion? Commented Oct 4, 2023 at 13:13
• constant voltage or constant current, pick one out of two. Commented Oct 4, 2023 at 13:20
• I used to charge my car batteries that I used in the test lab with my 30V/5A bench-top linear power supply by adjusting the output voltage to the max battery voltage (14.4V) and the current limit to something and then applying across the battery leads directly. This still can be used for Li-based batteries (although I don't recommend unless you know what you are doing) but shouldn't be the only way to go i.e. use if you are desperate or out of options. You still should clearly state the chemistry and type for better responses. Commented Oct 4, 2023 at 13:32

The charging conditions are dependent on the cell chemistry. This website contains very detailed information about all kinds of batteries: https://batteryuniversity.com/articles

# Example Li-ion

You can't have a constant current and a constant voltage at the same time. (Well, It can only happen if the load is constant.) This is because the voltage changes as the battery charges. However, you can limit both the voltage and current. By doing so, the charging process goes through various phases. Let's examine this by taking lithium as an example. Consider a scenario where the maximum current is set to 1A, and the maximum voltage is set to 4.2V. (Also shown in the graph below.)

When the battery is at a low charge level, the voltage is below 4.2V. Upon connecting the battery, the current will jump to 1A. During this initial phase, the battery undergoes charging in constant current mode. The voltage of the cell gradually rises. Once the voltage reaches 4.2V, the charging mode transitions to constant voltage. Throughout this stage, the current steadily decreases until it approaches zero, indicating that the battery is fully charged.

# Conditioning

When the Li-ion cell voltage is really low, it's not a good idea to immediately start at the full charging speed. This gives stress on the cell and reduces its lifespan significantly. In this case, It's best to charge at a very low speed. Once the voltage is large enough, you can start charging at full speed.

# Balancing

All this info assumes your battery consists of a single cell. When you have a battery pack that has multiple cells in series you have to monitor all cells individually to ensure single cells don't exceed the 4.2V.

In general, no.

You can't have constant voltage and constant current in a load that is varying. And a battery that is charging up isn't a constant load. It's electrical characteristics will change as it goes from flat to fully charged.