[jmpe]

That's for a large part due to the charging speed itself. If you charge at the maximum allowed current your battery will have the shortest longevity. Most chargers advertise on the capability to charge fast, but for a lot of battery chemistries it comes with that trade off. If you have the habit of charging over night I'd suggest to buy a slow charger or trickle charger. The slowest (optimum longevity) are typically "40 rate" which means (I'm simplifying here) the charge current is 1/40 the Max capacity current and takes about 40 hours to charge.

Note: don't go cheap by buying Chinese crap for battery chargers, especially Li chemistries. Best case: works as advertised. Worst case: electrocution or house goes up in flames.