Reliability of electronics in Li-ion battery devices

Yes.

No, I have never had one fail.

All batteries fail. You did well to get 12 & 15 years from them.

It's not the batteries I am asking about. It's the charging/discharging electronics, in the devices connected continuously to the charger when they are not being used. I have a 9-years old 18V Li-ion drill which is fine, but the batteries are only connected to the charger when I need to use it. We have another Li-ion battery-powered vacuum cleaner permanently in its charger cradle. It's a couple of years old now, and I wonder if it too will fail within another couple of years or so.

NiMh are not infinite life batteries. All my RC transmitters that had been boxed for 5 years without a charge needed new ones.

Sorry - my last post assumed NiMh.

Li-Ion have also limited life and the older the batteries are the faster they used to fail. Like electrolytic capacitors they have a gooey electrolyte that can dry out

There is nothing intrinisically wrong with the charging electronics, only that the reliability of the charging electronics depends on the quality of the charging electronics. Like power supplies everywhere, you can get top-spec units and ones where corners have been cut on spec and safety. It is also possible that you're using them contrary to the design (eg if the manual says 'remove battery from charger once full').

It is quite possible for the battery to disconnect itself from charging once it's fully charged, so as not to be continuously pumping charge into the battery. But it's also possible that a dumb charger/BMS is just holding the output at 4.2v per cell, which isn't something you want to do continuously.

Just like there were fancy NiCd chargers, and ones composed of a transformer and a resistor, you get what you pay for.

Theo

The lithium chargers don't generally trickle charge. That would lead to overcharging.

The rules are pretty strict for the design of such, because of the risk of fire.

If the charger would stop at 80% full, that would extend the service life of the product. Stopping at 80%, roughly corresponds to stopping the charge process just after Stage 1.