"... the charging circuit is, to put it mildly, primitive. There is no charging indicator. Nor is there a sign that the batteries are fully charged. The HX-20

"... the charging circuit is, to put it mildly, primitive. There is no charging indicator. Nor is there a sign that the batteries are fully charged. The HX-20 manual states that empty batteries should be put on charge for 8 hours. Leaving them longer risks damaging them, but without any way to tell that they are full there is no way to be sure you’ve timed it right. " This is normal for NiCd and later NiMH batteries. They're recharged applying regulated (ideally constant) current for a given time, and it's impossible to get a figure of their charge status just by sampling their voltage like with Lithium cells, which are dangerous indeed if abused, still much much easier to recharge. The only known ways to check those cells status are to either continuously sample the energy put in, or to intercept the so called delta V and delta T, a very slight (millivolts) decrease in cell voltage near the end of charge, paired with an increase of temperature which indicates the cell can't store more energy. This becomes even more difficult with battery packs, and makes measuring their status very hard when charging, and completely impossible if kept in use at the same time. Many portable safety anti-blackout lamps from the 70s to the 90s used NiCd and NiMH batteries, and many of them broke after some time because they kept their batteries under constant charge.