I'm not an expert on Li-Ion batteries but there are those who believe that they should not be routinely charged to 100%. Those chargers that show 100% but have actually charged to 80% may be prolonging the life of your batteries.
I drive an electric car (an iPace) and the advice I have received is to avoid charging the Li-Ion battery pack beyond 80% or so, except occasionally to balance the cells or immediately prior to a long journey. Apparently always charging fully will shorten the battery's life.
Does this apply to camera batteries? Maybe someone with expertise in this area can comment.
Bill
With Li-ion batteries, charging to 100% is perfectly fine as long as you are expecting the design of 400-500 cycles. Some charge systems (Sony is famous for their "Stamina" battery life extender) will allow you to charge to a lower capacity to increase cycles. Also, keeping a battery at 100% or below 20% constantly can be bad for the cells, but not regular cycling of the battery. It's actually better to constantly "use" the battery, charging it often.
It makes sense on expensive batteries (such as a car) to under-charge to increase life span. But, not on these old-assed design batteries that don't even have a cell balance feedback pin. I'll use the battery for 500 or so cycles and buy a new pack for $50-70 as needed. They are consumables. The TDM on the Dolgin is nice as it can cycle the cells to indicate the true charge level and allow me to determine when it is at a capacity where I feel it needs replaced.
Also, it makes no sense for the charger to under-charge, as it should then read less than 100%. The voltage at cutoff and cutoff current would also not be where it is. It's purely a crappy charger in this case, cutting off the charge prematurely and telling me that it's 100%. Rather, it's that the charger has some hard-coded passive cutoff instead of actively determining cutoff based on CC and CV. The knockoff no-name chargers are even worse. And, if it was "designed" to undercharge, the 100% on the Hahnel would always be xx% on the Dolgin, not sometimes 80%, sometimes 90%, and I've even had a few 70% during my tests.
If one was designing to under charge, it would be best to give the user the option to full charge or undercharge. And, then to show the proper capacity. Lenovo laptops have a setting in Vantage that allows the user to declare the charge start/end percentage. It's nice for laptops that live on docks all day with only the occasional mobile usage. But, those are proper and if set for 80%, will show "80% Not Charging" to indicate to the user the setting.