Why it stopped charging
Rechargeable toys rarely fail at the motor. They fail at the charging port, and there are only three reasons it happens. Two of them are worth trying to fix.
Three causes, in order of likelihood
Almost every "it will not charge any more" ends in one of three places: water got past the flap and corroded the board, the charging contacts oxidised and stopped making good contact, or the cell was left flat for long enough that it over-discharged. The first is terminal. The second is usually a two-minute fix. The third sometimes recovers and sometimes does not.
The flap, which is usually the answer
If the toy has a rubber flap over a USB socket, and it has been opened with wet hands for a year, assume water ingress until you have ruled it out. The symptom is specific: it charges intermittently, or only at certain angles, or it charges but the light behaves oddly. Corrosion on the board is not something you can clean at home, and it is not worth paying someone to fix on a toy at this price. This is the failure that magnetic charging exists to prevent, and it is the single best argument for paying a little more up front.
The contacts, which you can fix
Metal contacts that have sat in a drawer for months develop a thin oxide layer, and that layer is enough to stop a charge. Wipe them with a dry cloth first. If that does nothing, a cotton bud with a drop of isopropyl alcohol on the contacts — not inside the port, on the contacts — will shift it. Let it dry completely before charging. This fixes more units than people expect, and it costs nothing.
The cell, which sometimes recovers
A battery left completely flat for six months or more can drop below the voltage its charging circuit will accept, at which point the toy refuses to charge because it does not recognise a battery. The trick that sometimes works: leave it on the charger for a full 24 hours, ignoring the fact that the light does nothing. If it is going to recover, it usually does within that window. If it has not by then, it will not.
What is not worth repairing
Anything with a sealed body and a corroded board. Anything still under a retailer's warranty, which is where you should go first rather than reaching for the alcohol. And anything where the fault is intermittent in a way you cannot reproduce, because intermittent faults on sealed electronics are not diagnosable without opening them, and opening them ends the water resistance permanently.
Preventing the next one
Charge it before it is completely flat rather than after, and do not leave it flat for months. Close the flap before it goes near water, not after. And when you are buying, treat magnetic charging as a durability feature rather than a convenience one, because that is what it is.
More guides
Is it actually waterproof?
IPX7 is a real standard and most listings quote it correctly. What it does not tell you is that the test is done in clean, still, cold water on a brand-new unit, which is not the situation you are buying it for.
Bringing it up with a partner
The conversation is usually shorter and less awkward than the version people rehearse in their heads. What makes it go badly is rarely the subject. It is the framing.
How to read a product listing
A listing is written for two audiences at once: the people who will check, and the people who will not. Once you can tell the two halves apart, most of the marketing stops working on you.