So many devices use AA and AAA batteries nowadays. If you are using rechargeables for your home remote control, thermostat, or whatever, you can throw in any old ones and when the batteries are low, just recharge them. But, when camping or roaming the backcountry, I want to know that I have good batteries. I'm sure most people have put a set of freshly charged batteries in a device, only to have it crap out in an hour or so of use... one of the batteries are bad and can't hold much of a charge anymore, and usually you can't tell which one is bad and which one is good.
There's quite a few things that would decrease a battery's capacity - overheating, quick charging, too many charges, getting damp, natural variation, age, among them. Well then, how do you tell good batteries that have lots of capacity from bad ones? I probably have 50+ batteries for all my random devices, and want to use the best ones that I know are good for my GPS and other devices, especially when a charger isn't exactly close at hand. For the last couple years, I have been using the Powerex Maha MH-C9000 WizardOne Charger-Analyzer.. whew, that's a long name. But this thing is the best charger period for AA and AAA. It holds and charges up to 4 AA or 4AAA at a time on independent circuits and is larger than most 4AA chargers due to the LCD screen readout below the slots and is much more than your run of the mill charger with the light goes on when charging and off when it's finished charging. It can analyze the power capacity of each battery, and the charging rate is variable. It has five mode choice selections when you pop a new battery in - CHARGE, REFRESH/ANALYZE, BREAK IN, DISCHARGEand CYCLE.
By default it's CHARGE, if you don't select a different one within a couple seconds, it starts charging automatically at a default charge rate of 1000ma. If you select charge before the couple seconds are up, you can then change the charging current. The lower the charge current, the longer it takes, but it is gentler on the battery, and will also charge to a higher capacity. 1000ma charge is the default and that is a standard charge rate, able to charge high capacity NiMH AAs in 2.5 hours from fully drained. It keeps track of each battery slot and will tell you the amount (in maH) it charged the battery when you popped in has finished charging. This is good info. but it won't tell you if a battery is bad, since the battery is likely to have had a partial charge when you popped it in so you won't know the full capacity... REFRESH/ANALYZE is what you want for telling the capacity of the battery.
REFRESH/ANALYZE charges the battery from whatever state it was in until it is full, drains it completely, then charges it until full. This way you can tell after the battery has completed cylcling, the exact capacity of each battery. It takes a while for this cycle to complete, but it's worth it to find out the exact capacity of the battery sometimes. You can also alter the default charge and drain rates from the default as well, to customize it for each battery. I do this with my batteries a couple times a year and sort them by capacities. I mainly use Duracell high capacity 2650maH AA batteries at the moment, so I sort them in three piles - anything over 2400 is great and I use them in my GPS and other backwoods and high drain devices(such as a camera flash). 2000-2400 are OK batteries and I save them for around the house use. Lower capacities than that I usually recycle them. I mark the batteries with different sharpie pen colors so I can tell which battery is which capacity, last I analyzed them.
BREAK IN mode is for brand new batteries. Gives them a few full cycles to 'season' the battery and get it charged to it's maximum capacity before first use. This one takes quite a while to complete.
DISCHARGE mode drains the battery - I don't use this one much.
CYCLE I use someties to try to revive batteries that are borderline. I'll cycle them 5 times or so to see if the capacity increases.
Anyways, this is a great charger and a good tool to have, one of only a few that can tell you the exact capacity of each battery and will break new ones in to get the most out of your battery. If you are going to have a charger, might as well have one that can tell you how good your batteries are, right?
Maha also offers other chargers - some will do up to 8 batteries, and some simpler car adapter travel chargers don't have an LCD screen in addition.
Oh, and by the way, some more battery info - standard NiMH batteries such as the Duracell ones I am using self drain pretty quickly after charging so you have to charge them right before using them, which isn't always easy or quick to do. There are new ones out recently that have low self-discharging rates, these will hold a 75% of their charge after a year. I just ordered a pack of Sanyo Eneloop XX batteries. These just came out a year ago and are the first high capacity low self-discharge batteries. Quite expensive right now (about $20 for 4AA), but if I like them, I may start switching over to them... I'll do a review on those when I use them a bit . Another FYI - there's three different types of Eneloops - Eneloop lite (low capacity), regular Eneloops (medium capacity), and Eneloop XX (high capacity).
