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Bad battery???? #5223385 09/26/19 06:54 PM
Joined: Oct 2005
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otis24 Offline OP
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Battery is an Interstate MT-78. Just about 3 yrs old. Battery charger shows 98% charged but only 6 volts. I unplugged the charger. Does this mean that the battery is bad?


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Re: Bad battery???? [Re: otis24] #5223392 09/26/19 07:01 PM
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mk378 Offline
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Connect the battery to another known-good, charged battery (e.g. in a parked car) with jumper cables. Charge them both in parallel for a few hours with a known-good charger. Disconnect the suspect battery and measure its voltage. If the voltage has not come up over 12 volts it's definitely bad.

If voltage is over 12 volts continue to charge the suspect battery for 24 hours or so with your known-good charger. Then load test it.

Re: Bad battery???? [Re: otis24] #5223478 09/26/19 08:42 PM
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JMJNet Offline
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Load test the battery, it is easier to do.
Just bring it to a part store including WM with auto center.


Last edited by JMJNet; 09/26/19 08:43 PM.

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Re: Bad battery???? [Re: otis24] #5223523 09/26/19 09:48 PM
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JHZR2 Offline
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6v 98%?!?

It might be tricked into thinking you’re measuring a 6v battery...

Re: Bad battery???? [Re: otis24] #5223543 09/26/19 10:23 PM
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Rand Offline
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charger probably is a "smart" charger that thinks its a 6v battery?

As mentioned jumper it with a good battery for a couple mins.. and then put the charger on.

the voltage on the bad battery needs to be higher so the charger correctly detects it.

if that doesnt work its time for a new battery.


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Re: Bad battery???? [Re: otis24] #5223622 09/27/19 02:17 AM
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wrcsixeight Offline
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The state of charge % as shown on most battery chargers, is entirely based on initial voltage when the battery was connected and the charger plugged in. There is no electronic magic going on where the charger delves into the battery and can see its state of charge or state of health, the voltage gives a general idea of the state of charge, but since full charge resting voltage can vary from 13.16 to 12.6 depending on the battery the whole % is relatively asinine, especially when the user takes it as verbatim.

IF the 6v/12v combo charger thought it was connected to a 6v battery and saw 6.00 volts it would NOT say 98% charged, as a 6v battery is fully charged in the 6.4v range. If it was a combo 6v or 12v charger and thought it was connected to a 6v battery measuring 6.00v it would say ~50% charged.

Use a real voltmeter on the battery terminals.

Do not trust the % screen on chargers, or the voltage for that matter, especially if it is a Schumacher. My Schumacher was so hideously wrong, even when the display still worked. The display no longer does, but the charger still works, I just use a separate voltmeter and ammeter to see what it is doing, mostly if I clicked the buttons enough times to choose the 2 or 12 or 25 amp setting as those buttons lights no longer function anymore either.



Re: Bad battery???? [Re: otis24] #5223690 09/27/19 05:53 AM
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atikovi Offline
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Originally Posted by otis24
Battery is an Interstate MT-78. Just about 3 yrs old.


No warranty?

Re: Bad battery???? [Re: mk378] #5223823 09/27/19 08:52 AM
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WyrTwister Offline
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Originally Posted by mk378
Connect the battery to another known-good, charged battery (e.g. in a parked car) with jumper cables. Charge them both in parallel for a few hours with a known-good charger. Disconnect the suspect battery and measure its voltage. If the voltage has not come up over 12 volts it's definitely bad.

If voltage is over 12 volts continue to charge the suspect battery for 24 hours or so with your known-good charger. Then load test it.


Good advice . More thorough advice than what I was going to write .

If you do not have a Volt Meter , you can pick up one good enough .

https://www.harborfreight.com/7-function-digital-multimeter-63759.html

Best of luck , :-)


Wyr
God bless
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