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Can I charge a 12V 71Ah Car Battery with a 12V 12Ah - 48Ah Charger? When I try the charger says the battery is full, but the charge indicator on the battery says empty.

  • Welcome to Motor Vehicle Maintenance & Repair! Is the charger meant for a car battery? – Pᴀᴜʟsᴛᴇʀ2 Aug 21 at 11:12
  • Hello! Yes, it is. – Oliver Humphreys Aug 21 at 11:20
  • What "charge indicator" is saying your battery is empty? – Pᴀᴜʟsᴛᴇʀ2 Aug 21 at 11:23
  • it's built into the top of the battery - Green for good, White for recharge, red for replace. the battery is a Yuasa YBXX3100. – Oliver Humphreys Aug 21 at 11:58
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    It turns out the battery was completely dead! I think that because there was no voltage, the Charger wasn't recognising it was attached to anything. The charger's needle points to full as defult, then moves to the level of the battery being charged, this lead me to think the charger was showing "full" when actually it was showing "nothing". I got a new battery, and everything is fine now. – Oliver Humphreys Aug 23 at 11:50
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You can perform maintenance or "float" charges with underpowered battery chargers, but performing bulk charges (i.e. if the battery is completely drained) can burn out microcontroller in the smaller-powered "smart" chargers, or worse, cause the release of Hydrogen gas from the battery.

In summary, you CAN charge it with a lower powered battery charger, but it's not recommended when the battery capacity is >20% over the maximum capability of the charger.


If the battery is a Sealed Lead Acid (SLA), try rocking it gently side to side and tilting it slightly (no more than 30-45 degrees) a couple of times. Do you hear any liquid? If you do hear a liquid inside, let it sit for 15-30 minutes after.

If you have a multimeter/voltmeter, attach that to the battery in the 20 Volts DC setting and see if the battery is 10.5V or over, otherwise you may need a new battery. If it's in the 13.5V range, it's fully charged. Additionally, after sloshing and letting it sit, look at the battery indicator on the top of the battery and see what it is indicating.

WARNING: Do not tilt the battery completely on it's sides or hold it upside-down!

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