Why it doesn't charge properly?

It is not a battery problem if he replaced the battery 4 times and still has the same issue. I returned the unit for a replacement. Several months later the exact same issue happened. The batteries are not the issue and should last at least 18-24 months before they start noticeably losing capacity.

I replaced my battery this time. It worked great for a few months and again with the same issue. Full charge and the next brush it stops dead within a minute indicating 0% on the battery.

I removed the battery and re-inserted the same battery. Voila, 98% charged.

There is clearly a design defect with this line. The same thing has happened with my wife's unit; the exact same pattern.

@johnczukkermann I do not see where it says that the OP "he replaced the battery 4 times". What you are referring to is an answers that was posted 6 months after this answer. Sure it could be a design flaw, but it can also be an issue with the firmware as well as the charge controller.

I had to return the IQ toothbrush 3 times and purchased different levels of the IQ but all will not charge after 2 weeks. So purchased a different brand all together. That they may have a recall.

Thanks for this guide. It was very helpful. A couple of minor corrections for clarity:

• "During reassembly, make sure it snaps back into place." (This is the corrected comma placement.)

• "In case the battery sits to tight in its recess…" (The correct word is "too," not "to.")

Again, greatly appreciated.