LED Emergency Light Losing Power Quickly

[Michel]

I have an old emergency light with an almost dead 6 volt 4 amp battery inside, so I switched it to 2 x 18650 (3.7v, 4800mah) = 7.4 volt 4800mah.

At first everything worked out fine, until it started to loose power very quickly. Now if I charge it for 2 days and try to use it at low power it only lasts for almost 1 minute.

I'm guessing the issue is with a capacitor, but I still haven't checked.

Any suggestions to what would the problem be? and if replacing the 7.4v batteries with 6v ones would fix the problem?

 

[sxdave]

I have an old emergency light with an almost dead 6 volt 4 amp battery inside, so I switched it to 2 x 18650 (3.7v, 4800mah) = 7.4 volt 4800mah.

At first everything worked out fine, until it started to loose power very quickly. Now if I charge it for 2 days and try to use it at low power it only lasts for almost 1 minute.

I'm guessing the issue is with a capacitor, but I still haven't checked.

Any suggestions to what would the problem be? and if replacing the 7.4v batteries with 6v ones would fix the problem?

I would not expect the 7.4v battery to work in place of the 6 volt part. I expect the charger within the emergency light would be incapable of charging the 7.4 volt battery. When you charge the battery for 2 days what charger are you using?

It sounds like you are changing battery technologies as the 6 volt battery is probably Lead acid or NiCd and the 7.4 volt battery is probably Lithium Polymer. Changing battery technologies like this is not a good idea generally as they require different charging characteristics.

Also the presence of 7.4 volts instead of 6 volts when the light goes into battery operation (on loss of supply) may not be acceptable to the emergency light.

 

[telectrix]

don't be a tight arse. buy a new fitting.

 

[Mike Johnson]

18650 batteries need to be balance charged, if one is charge more than the other they will try to equalise and this could discharge both, its almost certain that the charger within the emergency light is not suitable for this battery chemistry.

 

[mainline]

I have an old emergency light with an almost dead 6 volt 4 amp battery inside, so I switched it to 2 x 18650 (3.7v, 4800mah) = 7.4 volt 4800mah.

At first everything worked out fine, until it started to loose power very quickly. Now if I charge it for 2 days and try to use it at low power it only lasts for almost 1 minute.

I'm guessing the issue is with a capacitor, but I still haven't checked.

Any suggestions to what would the problem be? and if replacing the 7.4v batteries with 6v ones would fix the problem?

Your charger won't be suitable to charge those batteries.

The 18650 The datasheet recommends a 1250 mA constant current charge, then 4.2 V constant voltage charge, and charge termination when the current drops to 50 mA

 

[Mike Johnson]

Eight months late with that, think the batteries would have given up by now.