Can Two Identical Chargers Be Connected in Series or Parallel? Feasibility and Risks of Using 12V 10A Chargers for 24V 50Ah / 12V 100Ah Battery Packs

  Many customers ask: Can two identical chargers be connected in series, in parallel, or in a mixed series-parallel configuration for charging? This article uses 12V 10A chargers and battery packs of 12V 100Ah and 24V 50Ah as examples to provide a systematic explanation.

Option 1: Two 12V 10A Chargers in Series (Charging a 24V 50Ah Battery Pack)

Conclusion: Theoretically feasible, but technically high-risk, and the actual output power will be compromised.
Principle and advantages: By connecting two chargers in series, the output voltages add up (12V + 12V = 24V), eliminating the need to purchase a dedicated 24V charger. If both chargers are identical and perfectly matched, charging can be achieved.

Key disadvantages:

- High voltage-balancing risk: The internal circuits of two chargers can never be perfectly identical. After series connection, uneven output voltage distribution easily occurs. One may output 12.5V while the other outputs only 11.5V, causing unbalanced charging of the two halves of the battery pack and damaging the battery over time.
- No isolation or protection: Once connected in series, the two chargers are no longer independent. If one stops or enters protection mode for any reason, the entire charging link is interrupted, and reverse current may even damage the other charger.
- Strict synchronization required: You must ensure that the charging parameters of both chargers (such as constant voltage value and cutoff current) are set identically; otherwise, safety issues are highly likely.
- Power derating: Taking a 24V 50Ah battery pack as an example, the series configuration can only deliver a maximum charging current of about 10A (current is equal everywhere in a series circuit), giving about 240W. A single 24V 10A charger also delivers 240W, while a single 24V 20A charger can deliver 480W. Series connection does not double the charging speed.

Option 2: Two 12V 10A Chargers in Parallel (Charging a 12V 100Ah Battery Pack)

Conclusion: Safer than series connection, but still not an ideal solution—low efficiency with hidden risks.
Principle and advantages: Connecting the outputs of two chargers in parallel adds the total current (10A + 10A = 20A), shortening charging time. If the battery pack voltage platform matches, it can be used for temporary emergency charging.

Key disadvantages:

- Current-sharing problem: The output voltage settings of two chargers can never be absolutely identical. The charger with a slightly higher voltage will carry most or even all of the current and may overload, while the other barely works. This causes one charger to run at full load long-term, shortening its lifespan, while the other sits idle.
- Lack of coordination: Two independent chargers cannot work together “intelligently.” Each operates on its own, which may cause the battery to repeatedly re-enter charging mode near full charge due to misjudgment by one charger, affecting battery life.
- Not battery-friendly: For a 100Ah battery, a 20A charging current is about 0.2C, which is within the normal range (below 0.5C is acceptable). However, given the instability introduced by parallel connection, it is more reliable to simply use a single 20A charger.

Core Recommendations

1. Series chargers are not recommended: Boosting voltage by connecting chargers in series is a case of “penny wise, pound foolish.” For a 24V battery pack, directly purchasing a matching 24V charger is the safest and most efficient choice.
2. Parallel chargers are not the preferred option: Unless for temporary emergency use, long-term parallel operation of two independent chargers is not recommended. If 10A charging feels too slow, upgrading directly to a 20A charger is a better choice.
3. Safety always comes first: Batteries have very high requirements for charging voltage accuracy. Using non-dedicated, non-matched charging solutions can easily cause frequent activation of the battery protection board (BMS) due to abnormal voltage, and may even lead to thermal runaway risks.