Contact the charger / battery is random. (With the original battery and with others from other manufacturers)

The charger connector with the battery really "cheap" (2 small vertical fingers that seem too small to properly get into the battery connector and very fragile, no comparison with the connector in the GoPro).

The good thing is that if the contact is not done this is easily notice the LED changing from green to red when charging. Stirring a little battery we finally have contact but this remains uncertain.

I checked (at 20 ° C) the final charge voltage with an accurate voltmeter: 4,22V it's really (too) close to the absolute upper limit (4,23V for techno LiPO) but ok.

I recommend the following non-yourselfers.
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For DIYers (at your own risk and void the warranty of course), you have to show a little (0.5mm) Contacts, which requires desoldering son, a little out the metal contact fingers and pick them behind (already as they hold!) to get a little more reliable contact. Note: The interface box is unclipped and disassembles easily (4 screws), it is already an assembly of a battery charger to be used for all batteries with a single LiPO element and a removable box that serves as interface between the charger unit and a size / type special battery (good idea to reduce costs but shame to have done so cheap adaptation for this battery).