6 volt led lantern

[yam]

I'm no genius when it comes to electronics, so please bare with me... I have a LED lantern that runs on 4 AA batteries. It also has a usb port that will allow you to plug into a laptop or usb output and power it as well. I wanted to extend the longevity of its use by wiring a bigger 6v 12ah NiCAd battery to it. I want to use it in a camper. I cut a old usb cord and I soldered an alligator clip to the red terminal (+) and the black (-). I then connected to the battery and plugged it into the lantern. The lantern will turn on, get real bright and then turn off. I assume it is a safeguard due to too much power. I put the AA batteries back in and it still works.... But I cant use the bigger battery. What am I doing wrong here?

 

[Resqueline]

It would be surprising if a simple thing like a LED lantern checks the USB spec (which is 4.75 to 5.25 Volts, or 4.4 to 5.25 Volts for low power devices).
Most of the cheap Chinese USB products puts out a far wider voltage range btw.. You can try if it helps with putting a 1N4001 diode in series with the NiCd battery.

 

[Zellarman]

assuming polarity was correct, what would the 1N4001 diode do?

 

[poor mystic]

The diode would provide a "forward voltage drop of about 0.6V", which means it would lower the voltage that the led lantern gets from the battery by a bit more than half a volt.