Battery Voltage Drop

[Sadlercomfort]

Hi Guys,

I have a battery which is supposed to show 6v on the output when charged, but is only showing 4v. I noticed that the charging voltage should be 7.2v-7.5v however the adapter which is being used has 6v output.

So just to verify, If i use a 7v adapter to charge my battery will my battery show the correct output of 6v?

Here's a link which shows the battery I have. It's an Aroma 6v 4AH Rechargeable VRLA 3-FM-4 (Lead Acid Battery).

http://www.kidsatplayextra.co.uk/kidsplay-6v-4ah-replacement-battery-a-151-p.asp

 

[(*steve*)]

It sounds like your battery has dropped a cell. It has (had) 3 cells, each nominally 2V. A 6V lead acid battery reading 4V is either very very badly discharged, or only has 2 working cells.

You might find that there is some swelling around maybe 1/3 of the battery.

 

[cjdelphi]

That or the charger has failed...

 

[(*steve*)]

That or the charger has failed...

Yes, that would be "very badly discharged". And at that level, likely undergoing a largely non-recoverable sulphation process.

 

[Sadlercomfort]

I see three cells none with any signs of bulging, how do I rule out the possibility of sulphation. Will a full charge cycle then a test again of the output voltage work?

It would good to learn how to test these batteries properly with guidance.

 

[Arouse1973]

Hi Sadlercomfort

Sulphation always happens in lead acid batteries but is normally reversed by fully charging. So if you have not charged the battery for a while or it never gets a full charge between uses then it's sulphated for sure. Whether it can come back depends on how long it's been stored in that state. If it's reading 4 volts with just a DMM connected, then this could be bad news. Fully charge the battery and then connect a smallish load say 100R across the battery and see if the voltage holds at all. If the reading drops quickly I would say if was naff.

A 6 Volt battery should read higher than 6 Volts when fully charged a good indication of near fully charged battery is 2.1 Volt per cell off load.

Adam

 

[Sadlercomfort]

Hey Guys,

I gave the battery a full charge cycle, including the appropriate extra time for efficiency losses. I now have a steady 6.2v.

Thanks guys!