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Safe, Fast, Flexible: The Maha C-401FS charger for AA NiMH cells

Reviewer: Dave Etchells
(Review posted: October 22, 2002)


* Charges AA or AAA cells.
* Use for NiMH or NiCd.
* "Smart" Charger, won't over-charge.
* Choice of fast (~100 minute) or slow/gentle (~8 hour) charge cycles
* Packed with cigarette lighter adapter for mobile use.


It's no secret digicams eat batteries, so rechargeable NiMH AA cells are a must if your camera takes that battery size. Regular visitors to this site will be familiar with my "Great Battery Shootout" page, where I've been systematically testing NiMH AA batteries under controlled conditions for almost a year now. (I'm writing this in mid-October, 2002.) In the course of that testing, I discovered that having the right charger is at least as important as having the right batteries. Some chargers overcharge and can damage the batteries, while others drastically under-charge, leaving high-capacity NiMH cells little better off than garden-variety types.

I've for some time been promising to undertake similar testing of battery chargers, but the press of too-much-to-do keeps pushing the charger testing to the bottom of the priority list. I'm getting closer to this though, and have actually run a few chargers through a preliminary test procedure, to evaluate charge time, completeness of charge, and maximum battery temperature. This current review is the first that will incorporate some of this more detailed information, although I haven't come up with definitive protocols for all parameters.

For a long time, my favorite batteyr charger has been the little C204F from Maha, which I reviewed back in Fall of 2001. This compact unit seems to strike an excellent balance between speed and completeness of charge, while avoiding "cooking" the cells as do some very high-speed chargers. The C-204F also comes with a cigarette lighter adapter cord for use on the road, and has a "conditioning" capability to help revive older cells.

Given how much I liked the C-204F, I was particularly motivated to check out Maha's latest charger, the C401FS, which seems to be positioned to replace the 204F in Maha's lineup. - Hence, this review, even though I don't have all my test protocols fully finalized.

The new 401FS drops the conditioning capability of the 204F (less needed for NiMH batteries than for the less-common NiCd types), but adds a couple of key features. First and foremost, it has four entirely independent charging channels, one per battery, vs the 204F's two. Having what amounts to a dedicated charger for each battery means that each cell will be optimally charged, extending the life of battery sets. It can often happen that an individual cell in a set of two or four may age faster than the other(s) in its set. When this occurs, a one or two-channel charger will unavoidably get the overall charge cycle wrong. - Either the weak cell will be overcharged, further shortening its life, or the healthy cells will be undercharged, significantly reducing the capacity of the pack as a whole.

The other significant advance in the 401FS is that it now offers options for either a 100 minute fast charge, or a very gentle ~8 hour medium-speed charge. This lets you manage the life of your battery packs better, using the gentle 8 hour charge for those times when you're not in a particular hurry, yet still having the 100 minute fast charge to fall back on when you need the cells charged right now. - And even the 100 minute fast charge doesn't seem to heat the batteries up as much as some "one-hour" chargers.

In the Box

The C401FS charger comes with the usual wall-wart power adapter, but also includes a cigarette lighter adapter as standard equipment. Very handy for trips! Internet battery experts Thomas Distributing also have a universal (US/European) power acapter for the C401FS, if you're going to be traveling to a country with 220v power instead of the 120v we have here in the US.


The PowerEx C401FS handles both NiMH and NiCd batteries, automatically detecting the two different battery types and adjusting its charging profile to match. It also supports any combination of AA or AAA batteries, thanks to two sets of contacts, and circuitry that reduces the charging current for AAA cells, to avoid damaging them.

As mentioned above, the C401FS has four independent charging circuits in it. Besides providing more accurate charging of each cell in a set, this comes in handy if you have a digicam that takes only two AA cells, because you can charge pairs of batteries independently of each other.


The C401FS is a "smart" charger, which means it applies a high rate of charge to the batteries when first inserted, then cuts back to a "trickle charge" when peak voltage is reached. Fast-charge current is 1000 mA per cell (500 mA for AAA cells), about as fast as you'd want to dump charge into typical NiMH batteries. Once maximum charge is reached, the charging current drops to 50mA, a nice, gentle level that can be tolerated for long periods by most good-quality NiMH batteries on the market. - It's thus save to leave batteries in the C401FS more or less indefinitely, helping avoid the "self-discharge" of NiMH cells that would otherwise severely limit shelf life.

The "smart" charging means you can safely use the C401FS to "top off" the NiMH cells from your digicam if you're about to head out with it, without worrying about over-charging them.

Depending on the capacity of the batteries you're charging, the C401FS in fast charge mode can bring a set of AA cells from "empty" to fully charged in right around 100 minutes. (Figure as much as two hours for the most recent high-capacity NiMH AAs.)

In slow-charge mode, the charging current is reduced to 300 mA, significantly reducing the amount of both heat and currentthe batteries are subjected to, thereby extending their life somewhat. - Once the cells are fully charged in slow charge mode, the 401FS drops to a 50 mA trickle charge to keep them topped-off.

Completeness of Charge

This is a new category for a charger review for me, although it's obviously a pretty critical one. I haven't included it in the past because I didn't have a reliable way to test for it. Even now, it's a little problematic, as I'm reduced to using "reference batteries" to test with, which is far from an absolute standard. My approach is to take a set of batteries that have been very well characterized from my battery testing, and then see how close to their maximum capacity a given charger can get them. (In my battery testing, I've found that a combination of a medium-fast charger like the Maha C-204F together with a low-rate DC trickle charge overnight brings cells to the maximum capacity attainable. - For some reason, the overnight trickle charge with fairly pure DC seems to "top off" cells more consistently than simply leaving them in a fast-charger that also has trickle-charge capability.)

I've been using some Sanyo industrial 1600 mAh cells as my "standard" batteries because they seem to have the lowest decrease in capacity from cycle to cycle of any I've tested. - They're by no means the current capacity leaders, but their heavy-duty construction seems to provide very consistent cycle to cycle results. Even given this ruggedness, there is still some decrease in capacity as the number of charge cycles increase, which I have to compensate for in evaluating the test data.

With that as background, I can report that the C401FS seems to bring batteries to a pretty complete state of charge in both its slow and fast-charge modes. Here's a digest of data collected over about 10 charging cycles, with the Sanyo 1600 mAh cells:

Maha MH-C401FS performance
(Based on Sanyo 1600mAh industrial cells)
Mode Charge
Slow Charge < 5 hours 97% 97 F
Fast Charge ~110 min 94% 133 F


Charge completeness numbers of 94% in fast charge mode and 97% in slow charge mode are pretty good, at least in my experience to date. (I haven't really found any chargers that do a better job than this.) I believe that the 401FS will take cells to very nearly 100% capacity if they're left in it overnight, to let the trickle charge "top off" the cells, but I haven't tested overnight charge cycles yet for this charger.


This is an odd heading title for a battery charger review, but it's an important one if you want to get the maximum life out of your batteries. Some chargers seriously overheat batteries, which can shorten their life. Some (pretty significant) temperature rise is normal in charging batteries, and shouldn't cause a problem. Too much will definitely lead to early exhaustion. In its "slow charge" mode (I'd really call this a "medium" charge speed, since there are many chargers on the market that run slower than the ~5-8 hour cycle of the 401FS in this mode), the maximum temperature of 97 F is very good. The batteries will feel warm when they're done, but aren't anywhere near what I'd call hot.

The 133F maximum temperature in fast charge mode does feel quite hot to the hand, but is still just within the spec most manufacturers set for maximum charging temperature, and isn't as high that produced by some one hour chargers. In the interest of maximum battery life, you'll want to use the most gentle cycle you can, as much of the time as you can get away with. Thus, if you can afford to wait, use the 401FS' slow-charge mode. If you do need your batteries in a hurry though, I'd say that the fast charge cycle is pretty safe.

NOTE: Run with the cover open!

It's important to note that the temperature readings above were obtained with the transparent lid of the 401FS flipped open during charging. This is VERY important for any charger with a lid on it. Don't run the charger with the lid closed, as this will drastically increase the peak cell temperature, with the expected effect on battery life.


It couldn't be much simpler - With the charger plugged into its power source, insert one, two, three or four AA or AAA cells in any combination, and away you go. The charger immediately begins charging the batteries, and the indicator LEDs light red. When the full-rate charging is complete, the LEDs turn green, and the charger enters trickle mode.

I generally leave my batteries in the 401FS after they're charged, to keep them topped off. Most good-quality NiMH cells can tolerate this just fine, as the 50mA trickle current is a pretty gentle level of charging. (Some battery brands may not be able to handle this, so be sure to get good-quality batteries so you can do this. - Of the batteries we've tested, we'd recommend Maha's own PowerEx brand, GP, Kodak, Nexcell, or Yuasa-Delta as all being good.) On the other hand, if you're not going to use your batteries for a long period of time (days to weeks), you'll be better off to remove the cells from the charger and store them in a drawer until you're about to use them. Then pop them back in the charger to top them off and you'll be ready to go. (NiMH cells lose anywhere from about 1-3% of their charge each day, depending on the quality of the cells, storage temperature, etc. - It's thus important to top-off any cells that have been lying around for a week or more since they were last charged.


Maha ships the Powerex MH-C401FS in "kits" with a set of four of their highest-capacity NiMH cells included in the box. A kit with the standard US-only power adapter (Maha part number MH-C401FS4AA18) carries a list price of $49.95, while the kit with the "universal" travel power adapter (Maha part number MH-C401FS4AA18W) runs $59.95. These prices are a bit higher than the earlier 204F model, but the availability of a fast-charge mode and fully independent charging circuits justify the increased price. (While Maha only ships the 401FS in kits with the batteries included, you may find some dealers offering it without the cells, at a lower price. - Handy if you're already stocked to the gills with AA NiMH cells, and are just looking for a better charger.)

Bottom Line

The C401FS looks like an excellent follow-on to my previous favorite charger, the C-204F. Even though I almost never used it, I do miss the conditioning capability of the 204, but the fully independent charging circuits and dual charge speed option more than make up for that. Overall, the C401FS looks like a nearly perfect battery charger for digicam enthusiasts. It lets you choose between a very fast charge cycle that's still safe for batteries, or a longer one that's very gentle. It's also quite compact and priced affordably. The 12v car adapter is an added bonus for trips and vacations.

Very highly recommended. - Don't think twice, if you have a digicam that uses AA cells, buy one of these and a couple of sets of high-capacity NiMH batteries. When it comes to compact battery chargers, the C401FS is about as good as it gets!


As I go through various chargers on the market, I'll rate them in various areas. Here's now the Maha/PowerEx C401FS stacks up:

Maha/PowerEx C401FS
Completeness of Charge
Gentleness (in slow charge mode)
Overall Score (5 out of 5!)

Purchase/More Info

Here's a link to a page at Thomas Distributing, where they offer a C401FS with a set of PowerEx 1800 mAh batteries at a very good price. Like we said, don't even think twice. - If you have a AA-using camera, this is the kit to get. Also available at



For more info on the charger, here are some links to Maha's site:

C401FS product page & Spec Sheet

C401FS User Manual (PDF format)