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I have a pocket bike 3 batteries. 12amps and 12 volts each. So 36v. My charger is a 36v 1.6amp charger output. The problem is the batteries get to 45v quickly even when dead. Then the charger shuts off because it thinks it’s full. Power only charges for 5-10 seconds of bike use. Is there a way to lower the voltage just 3-5 v to charge them properly without buying anything and re-wireing things to trick the charger to do a full charge?

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closed as off-topic by duskwuff, Finbarr, PeterJ, RoyC, Michel Keijzers Mar 8 '18 at 17:15

This question appears to be off-topic. The users who voted to close gave this specific reason:

  • "Questions on the use of electronic devices are off-topic as this site is intended specifically for questions on electronics design." – duskwuff, Finbarr, PeterJ, RoyC, Michel Keijzers
If this question can be reworded to fit the rules in the help center, please edit the question.

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    \$\begingroup\$ Seems to me more like a battery problem than a charger problem. \$\endgroup\$ – brhans Mar 6 '18 at 21:36
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    \$\begingroup\$ Sounds like the batteries are sulfated. Did you leave them unused and discharged for several months? A sulfated battery will appear to charge quickly, but will be unable to deliver much current, as only a small portion of the plates will be active. \$\endgroup\$ – Peter Bennett Mar 6 '18 at 21:42
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    \$\begingroup\$ That's in fact the answer, Peter. Post it as such. \$\endgroup\$ – Janka Mar 6 '18 at 21:43
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    \$\begingroup\$ All it takes is one bad ( sulphated) cell out of 18 \$\endgroup\$ – Sunnyskyguy EE75 Mar 6 '18 at 21:53
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45 V is charged for a "36 V" lead-acid battery. In fact, that's overcharged.

If the battery is getting to 45 V quickly even when you know it's low, then the battery is really dead. Maybe one or two of the 12 V batteries are still OK. Try charging the batteries each individually with a 12 V battery charger. Almost certainly at least one of them will appear to be full immediately. Those are dead. Dispose of them properly.

If these three 12 V batteries were always used and charged together, then you really should replace all of them. Even if one or two still appear to work, they have all probably been abused or are old.

It's time to get new batteries.

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  • \$\begingroup\$ The batteries are only 2 months old. \$\endgroup\$ – Daniel Stamatoiu Mar 6 '18 at 23:52
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    \$\begingroup\$ Then between "abused or old" we'll choose "abused" - excessive discharging, improper charging, overcharging, many ways to kill a battery in the prime of youth. \$\endgroup\$ – Ecnerwal Mar 7 '18 at 2:09

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