So after having some wet weather related problems, I sealed the battery with liquid tape, extended the cable and put the battery in my waterproof pannier. It worked fine for couple of weeks. In the last few days the connection become intermittent. I would unplug it and plug it back and it would work for a bit. Today, it stopped working completely. When I plug the light in it just blinks and dies, no light, no LED. It seems like connector problem, but it is not.
I took the battery apart. There is a small circuit board attached to it and that circuit board is the problem, not the connector. I un-soldered the cable from the circuit board, cut off the connector from the light and connected bare wires from the light directly to the circuit board output where the wire was soldered: the same thing, the problem persists. If I connect the wires directly to the battery output, bypassing the circuit board, it works fine. Also, if I connect the light to a 6V power supply it works fine, so the light is OK.
So I wonder if there is any way to obtain that circuit board, I believe it's needed for charging. Otherwise, I'll just get another battery, but not the same. Has anyone found a reliable battery replacement? It can be larger, that's OK and obviously I don't mind soldering the connectors. I've found many on the net but I'd like to know if anyone actually has a good working alternative that was tested under normal use.
Edit: To clarify: both the battery directly and the circuit board provide stable ~8.3V without load, when the only thing connected is the multimeter. The problem lies in the circuit board failing under load. If I connect the light, while the multimeter is connected at the same time it shows that the voltage instantly drops to ~2V the moment the light is connected.
The battery that comes with MagicShine is 4000mAh, 7.4V rated at 1.5A. I believe the light will work with any battery that supplies 6V to 8.4V and can deliver 1.5A. However, 7.4V is recommended.
Happy New Year everyone!