Several years ago, I picked up an interest in rechargeable batteries because I think they offer so much convenience and value for money over normal disposables. It may be more expensive at the start, but subsequent re-charges brings down the cost way below disposables. With today's high drain devices such as cameras, handphones and torch lights, rechargables actually outperform branded alkaline batteries.
Rechargeables batteries, while they are very good, they demand some care in order to maintain their high performance. One of the most basic way is to choose a good charger. To make things difficult, not all branded chargers are good.
Here, I'll list down the crucial features you should be looking for:
1) Charging speeds come in a few flavours.
15min "high speed" charger
These are speedy chargers that often come with a 15min timer. They are really good if you need to recharge your batteries in a rush, but they are very bad for your batteries. Charging at such speed forces a lot of current into a small battery and in turn, they get extremely hot. These chargers fry your batteries with every charge and you won't get much battery longevity using these.
Overnight chargers
Ok, so fast chargers are bad, so slow chargers should be good then? Nope. Overnight chargers are typically "dumb" chargers - they do not know when a battery is full, so manufacturers use very low current to charge the batteries. Adding more energy into the battery after it is full also causes the battery to wear out faster, but not as much as those 15min fryers. Overnight charging is just too long! Who waits that long!
~2 hour "fast" charger
These chargers are often able to detect when a battery is full and stops right there. A 2 hour charge is actually the optimal charging duration because it is slow enough such that the battery does not get too hot during charging and it is fast enough for an accurate battery charge detection.
2) Battery charge detection
Built-in timer (no detection)
By far the worst type. You either end up force feeding your battery or end up with a partial charge.
Temperature
Not accurate at all. Batteries typically rise in temperature as they reach full charge, but detection is difficult.
Negative Delta V detection
Ni-MH batteries dip slightly in voltage when the battery is full. When the charger detects this dip, it stops the charging. This is extremely important because it is able to charge up a high capacity battery and/or partially depleted battery to its full capacity, every time.
3) Dual cell charge / Single cell charging
Manufacturers sometimes try to save cost by charging 2 slots at once. This means that you'll need to put in 2 batteries before it charges both. This is terrible because batteries may have started off with an uneven charge. So, it is important to choose a charger that has dedicated slots for each battery!
So, after saying so much, do I have a recommended charger?
If you don't mind spending more for a sophisticated charger that does a lot more, get a Maha Powerex MH-C9000 analyzer/charger. Be warned, you'll get to set your own charging rate. At about sgd$100, you get features to break-in new batteries, run capacity tests and more.
Otherwise a $30 Ikea LADDA battery charger is actually very good. It was reviewed in Candlepowerforums. It comes with all the basic features of an excellent charger. At $30, you won't find other chargers that can match it. It's nice to discover hidden gems which are not well marketed but are actually very good.
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