have the Maha MH-C-124S overnight charger. How do I know when the batteries are fully charged?

have the Maha MH-C-124S overnight charger. How do I know when the batteries are fully charged?

The Maha C-124S has a couple of advantages but it does require some monitoring of the charging process. The advantages are that it provides a constant gentle 50-70mAh charge current which will extend the cycle life of your batteries (see FAQ above). It also has 4 independent charging circuits so you can charge any combination of cells. Most NiMH chargers require batteries to be charged in matched sets. You can charge one, two, three, or four cells of any type (NiMH or NiCd) size (AA or AAA) or capacity rating since it provides a steady charge to all 4 circuits. If you need to charge an odd number of cells (one or three) then this is the charger for you.

Charging with the C-124S requires some planning. You will be charging your batteries with an average current of 60 mA per hour or mAh. To determine how long to charge your batteries fully simply divide the required capacity by 60 mA. For example; fully discharged 600 MAh capacity AAA batteries will require approximately 10 hours charging time (600/60) and fully discharged 1800 mAh capacity AA batteries will require approximately 30 hours charging time (1800/60). If you are charging 1600 mAh batteries that are only 50% discharged it will take around 13-14 hours. See the charging chart on our Charger Manuals page for further guidance.

One significant advantage of this charger over other slow chargers is that you can safely leave the batteries in the charger beyond the recommended charging time without damaging them. Other slow chargers provide a higher charging current and shut off with a timer. The timed charge of these other chargers is only a guess and you could easily overcharge your batteries. (If you significantly overcharge your batteries you can damage them internally and reduce their ability to hold their rated charge capacity).

Note: Even though the C-124S provides a gentle charge current you can eventually overcharge your batteries if you leave them in the charger for too long. Maha recommends removing the batteries from the charger within 72 hours of the time they were fully charged. Your NiMH batteries will then self-discharge at the rate of around 1-2% (15-35 mAh) per day even if you don't use them. If you want to "top off" the charge on your batteries before you use them put them back in the charger to regain the lost charge.

Tip: If you don't want to worry about overcharging your batteries then purchase a smart charger which electronically monitors the battery charge condition. Smart chargers will sense when the batteries are fully charged and provide several different protections against overcharge/overheating as well as automatically switch to a trickle charge when charging is complete.