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My Ebike uses a 48v battery, but the charging amperage listed on the side is 2A, and the original charger likewise is 2A. Having lost that charger, the replacement I could get on short notice is a 4A charger. Will it be safe to use a charger giving double the amperage?

Battery: FuturePath "48-19.2 Li-Ion battery" Original Charger Model: DPLC110V55 Replacement charger: https://www.amazon.com/dp/B08SKKQQ15?psc=1&ref=ppx_yo2ov_dt_b_product_details

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  • There is no way for us to determine this. Probably OK, though, and if someone were anal they could insert a resistor in the circuit.
    – Daniel R Hicks
    Commented Jun 25, 2022 at 12:24
  • If limiting current with a resistor, it would have to be a big honking resistor. Resistors operating at several amperes will dissipate many watts of power. It will get hot. Not every resistor can handle this heat. Also a resistor is not ideal for current limiting purposes. Something like a measurement circuit with Hall effect sensor or a small sense resistor controlling with an operational amplifier the base current of a transistor would be much better. It would be actually constant limited current unlike with a resistor.
    – juhist
    Commented Jun 25, 2022 at 18:14
  • If it’s rated at 2a the most it will pull is 2a whether you use 4a or 2a. It would even charge with 1a but slower. There’s a common misconception it will charge quicker will higher amps but it won’t as it will only draw the max of 2a
    – Dan K
    Commented Jun 26, 2022 at 8:28

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Most likely it will be safe.

In most cases, lithium ion batteries contain a safety circuit that controls the charging. The charger in this case will be a constant voltage current limited charger.

I assume the safety circuit in the battery will kick in if you attempt to charge it unsafely.

If this is the case, you can pick any charger that has the same voltage and at least the same current. Lower current chargers might work but limit the charging speed.

This applies to batteries that have a safety circuit. Batteries such as lead acid and nickel metal hydride batteries do not have a safety circuit. Lead acid and nickel metal hydride require limiting the charging current at the charger. Lead acid batteries are charged with a constant voltage current limited supply where the current limitation has to be below that of the battery and the voltage is the absorption voltage, then when nearly full with the same supply but the voltage set slightly lower (float voltage). Nickel metal hydride is charged with constant current and with battery chemistry specific end of charge detection (usually with voltage limitation, voltage negative derivative and temperature limitation plus a timer limitation often as well). With nickel metal hydride you have to understand as well that end of charge detection with voltage negative derivative is unreliable at slow charge rates, so charge rate has to absolutely be between 1 and 2 hours or you'll reduce the life of your battery. But those chemistries aren't used in e-bikes.

However, in theory it's possible the specific battery and charger combination is designed in such a manner that the battery doesn't have current limitation in the safety circuit and it's the job of the charger to limit current. This would be fairly unusual, but I can't be certain some cheap Chinese brand wouldn't do this.

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  • Used it twice to recharge the battery from low, and it works with no issues.
    – Toshi
    Commented Jun 30, 2022 at 10:28

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