High Voltage
I just upgraded to a charger with a digital display. When charging, the voltage reading on the charger is higher than the rated voltage of the pack. Is the charger overcharging the batteries?
Your charger is working fine. Batteries have a nominal voltage that will be equal or close to what they’re labeled at when the pack has been sitting for a while. But as you discovered, voltage will display higher than what’s on the pack’s label as the battery charges. And after charging, if you check the pack’s voltage with a voltmeter or voltage checker, you’ll note that it’s higher than what the label says.
When set for NIMH batteries, a charger will allow voltage to climb until its software detects that voltage is no longer rising. This signals the pack is fully charged, and the charger stops. When set for Lipo batteries, the charger will stop charging when each cell reaches 4.2 volts, which is the maximum safe voltage for Lipo cells. That’s why it’s so important to choose the right mode when charging batteries. If you “tell” your charger that it’s charging a NIMH pack but it’s actually a Lipo, the charger won’t stop at 4.2 volts per cell—it will keep charging as it waits for the voltage to stop increasing, which at a minimum will damage the battery and will quickly lead to a fire if not caught in time. So DO be certain to choose the right battery-type setting for your charger, and DO NOT leave it unattended while charging. But don’t worry if the displayed voltage is higher than what’s on the pack’s label; that’s totally normal.