Nextgen battery heated and smoked without outside electrical current.

I have two TVs in the same room using Verizon FIOS multi room DVR. The FIOS remote control is not paired to a FIOS box, so changing a channel for one TV, changes it for both. Same for pause, FF, etc. Not what I had in mind.

A friend described a solution that he got three years ago:

This device converts a regular remote into a radio signal remote. You then cover the light signal on one remote and one box with black tape and one remote is now light-activated, the other one radio activated, so they don't interfere with each other.
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I checked it out and ordered the Next Generation Remote Control Extender directly from nextgen.us.

After it arrived I wrote this to my friend:

I put one of its little batteries in the base (flying saucer) to charge the battery and before I could plug it into the electrical outlet, the battery started to heat up and was smoking. I had a difficult time extracting the battery and it was HOT.

I never plugged in the "flying saucer".
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I then wrote to Nextgen:

order number is nnnn: battery smoked!

from: Ken
to: customercare@nextgen.us
date: Sun, May 7, 2017 at 4:43 PM

I received your product yesterday: Remote Control Extender.

This morning I put one of your little batteries in the base (flying saucer) to charge the battery and before I could plug the flying saucer into the electrical outlet, the battery started to heat up and was smoking. SMOKING! I had a difficult time extracting the battery because it was HOT.

I also inserted the single IR (infrared) emitter cord into the back of the unit before inserting the battery. The bottom compartment of the flying saucer has an A-B-C switch that was set to B. I did not see any instructions for it and left it at B.

I never plugged the "flying saucer" into any electrical outlet. Still haven't. Your special battery and/or your flying saucer base are defective.

​I left a voice message for Bob at 727-834-9400.

What the heck?
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I never spoke to Bob, the big expert at Nextgen, after the battery smoked. Nextgen did not seem alarmed, which I found alarming. No explanation was provided. Today I received my refund.