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What is the best rechargeable battery charger??

I am asked this question several times a week. My answer, it depends. What are you going to use the charger for??
Let me share some information that should help you pick a good charger for you needs.

Ground rules. This discussion will deal only with NiMH batteries and chargers.

First let me talk a bit about charge rates. In order to have a well defined knee in the charge so that full charge can be detected by a -dV algorithm it is best to charge NiMH batteries at a sufficient rate. When battery people talk about charge rates they usually throw around a bunch of "C" numbers like .2C or .5C or even 1C. So what is "C" and what does that have to do with the charger you select.

In simple terms you can get "C" by taking the battery capacity in Ah or mAh (explained in a moment) and divide out the time or hours (h). So if we have an AA cell that is rated at 2700 mAh in order to find the 1C rate we divide the mAh by h and get mA (miliamps or thousandths of an amp) So the 1C rate for that cell is 2700 mA or 2.7 A. In theory if you charged that cell at the 1C rate for an hour it would be close to fully charged.

I do not recommend charging at such a high rates for consumer AA and AAA cells. The problem is heat. When the cells are charged at high rates such as 1C or more it is very easy to get too much heat build up in the cell. If it gets so hot that the cell vents gas then it is now on it's way to premature failure. It is possible to charge at those rates but only with the right charger that monitors the batteries for all parameters to prevent any damage to the cells. It would also be best to use active cooling for the cells being charged.

Having said those negative things about fast charging at 1C or higher rates I also have to say that it there is a problem with charging at very low rates. As mentioned above very low rates may not give the indications needed in the charge curve to show when full charge has been reached and the charger will fail to terminate charge properly. In short the charger can miss the -dV charge termination point. So very slow charging is not really a problem with the batteries, it is a problem with the chargers as they may not be able to detect full charge conditions.

So what is the best charge rate?? I recommend chargers that normal charge in the .2C range and fast charge in the .3C to .4C range. Those are rates of charge that are high enough for the charger to work well and not so high as to cause undo heating in the cell being charged. Here is an example. Suppose you have some NiMH AA cells rated at 2500 mAh. The 1C rate for those cells is 2500 mA or 2.5A. The normal charge rate .1C to .2C would be 250 mA to 500 mA. The fast charge rate .3C to .4C would be 750 mA to 1000 mA. In that case a charger that charges at 500 mA would be perfect for normal charging. It would charge those 2500 mAh cells in a little over 5 hours.

Let me summarize. The best charger is one that is computer controlled and has independent channels for each battery being charged. It detects full charge with a -dV algorithm. It has temperature monitors for each battery being charged. It normal charges at .1C to .2C rate or it can fast charge at .3C to .4C rate. It should set appropriate rates for AA or AAA batteries automatically.

Here are some chargers that meet those criteria.
PowerEx MH-C800S. Very good consumer grade charger.
PowerEx MH-C801D. Good professional grade charger, higher rates faster charge times.
PowerEx MH-C808M. Professional grade charges AA, AAA, C, D.

Chargers that can test batteries for capacity.

Say you purchase some batteries that are billed as the latest and greatest AA 3000 mAh batteries. How do you know?? Most major brands are very good about rating their batteries, they supply standard data sheets on their web site. However there are manufacturers and retailers that flat out lie about the capacity of batteries. So how can you tell if you are getting ripped off. Get a charger that can actually test batteries for capacity.

First a bit about battery capacity. Capacity rating is usually given in Ah or mAh (Ah - amp hours or mAh - miliamp hours) and is an indication of how much energy is usable from the battery. An example, if we have an AA cell rated at 2500 mAh it means that battery could supply a 2.5 Amp load (2500 mA) for a time of one hour. Or it could supply a 500 mA load for a time of 5 hours. Approximately. So capacity is an indication of how much work you can do with your batteries.

There are chargers that can test your batteries for the actual capacity, as opposed to what is claimed by the manufacturer or retailer. To do this all of these chargers perform the following cycle; put a full charge on the batteries, then perform a controlled discharge while measuring how much energy is obtained from the battery, then perform a full charge again. At the end of the cycle the tested capacity is displayed on the control panel of the charger. If you are serious about getting the best performance from your batteries then this kind of charger is a must have. It is the only way you will know for sure the state of your batteries.

These kind of chargers usually have other functions that are useful such as break-in and recondition cycles. Names and details differ but the ability to test is the same in all of them. Some have better capability and controls than others but the ones listed here will all do the basic job of testing batteries for actual capacity.

Shown in table form with basic parameters.

Brand Max Charge Current
Max Discharge Current
Max Chargeable Capacity
PowerEx C9000
2000 mA
1000 mA
19.99 Ah   (19,990 mAh)
Opus BT-C2000
1000 mA (1400 mA @ 2 cells)
500 mA
20.00 Ah (20,000 mAh)
1000 mA (1400 mA @ 2 cells)
500 mA
20.00 Ah   (20,000 mAh)
AccuPower IQ328
1000 mA (1800 mA @ 2 cells)
500 mA 3500 mAh
La Crosse BC-1000
1000 mA (1800 mA @ 2 cells) 500 mA 3000 mAh
La Crosse BC-9009 (same as BC-1000 no longer sold)
1000 mA (1800 mA @ 2 cells) 500 mA 3000 mAh
La Crosse BC-700
700 mA
350 mA
3000 mAh
La Crosse BC-500
500 mA
250 mA
3000 mAh

As you can see the PowerEx C9000 is has the highest current capability in this group. The charge and discharge functions are programmable in 100 mA increments. It is well constructed with good ventilation for the batteries under charge. The firmware allows charging and testing high capacity cells unfortunately the C&D adapters do not always work well in this charger due to contact resistance issues. Good for AA and AAA NiMH, NiCd cells.
MH-C9000 $49.95

The BT-C2000 is the best overall. It is the easiest to use even if only adjustable in 200 mA increments. All four channels can be set up easily. And yet you have the option of changing any channel program at any time. The C&D adapters come with the charger so it can handle high capacity C and D cells out of the box. Testable capacity 20,000 mAh. Best overall pick.
BT-C2000 $49.95.

Next in line the BM200 is a capable charger. It has good space for cooling the batteries under test. The charge rate is programmable in 200 mA increments. The discharge rate is fixed at half the charge rate for capacity testing. Same testable capacity as the C9000. This charger also has a test for battery internal resistance. This can be a useful test for some applications. Ships with C&D adapters for charging and testing high capacity C and D cells. No longer in production, limited to stock on hand. Replaced by BT-C2000
BM200 $29.95

The AccuPower IQ328 is more compact, gives less cooling air to the batteries. The charge rate has 4 settings, 200 mA, 500 mA, 700 mA and 1000 mA. The discharge current is fixed at half the charge current. Maximum testable capacity is 3500 mAh firmware restricted. A capable charger and good value.
IQ328 $29.95

The La Crosse BC-1000 and BC-9009 are identical, except for the color of the case. The BC-9009 is no longer produced. These two chargers have the same electrical specifications as the AccuPower IQ328. Four charge current settings, 200 mA, 500 mA, 700 mA and 1000 mA. Discharge current is fixed at half the charge current. However firmware restricts testable capacity to 3000 mAh.
BC-1000 $59.95

The La Crosse BC-700 is just like the BC-1000 except it has only three current setting, 200 mA, 500 mA and 700 mA. Discharge current is fixed at half the charge current. 3000 mAh max testable capacity.
BC-700 $34.95

The La Crosse BC-500 is the most limited. The display is limited in the information it can display and charge current is 200 mA or 500 mA. It has only one function button and is a bit harder to program and use for test purposes. If is not a good choice for testing batteries.
BC-500 $29.95

There are other clones of these chargers available, such as the Technoline BC-700. These have specifications and operation identical to those noted.

Battery test information

What are the best batteries??

How do batteries compare??

The first column displays test results from battery analyzer tests. This device allows testing at selected current load. Time, Voltage and Current are logged. Results are  battery discharged capacity (mAh) and discharged energy (mWh). For all NiMH cells the test termination voltage is 0.90V. The test current for AAA and AA cells is 500 mA. Test current for C and D cells is specified in the test results. This allows comparison of the cells with no other factors influencing the results as may be the case in the testing charger results. This can be compared to the results from the individual charger tests to see how the chargers perform. Note; only the C9000 and BM200 are capable of testing the C and D cells with adapters. This is due to firmware restrictions in the La Crosse Techology and AccuPower chargers.

I use the chargers available with a test function. This function displays the actual capacity of the cells under test. All of the chargers perform this test basically the same way. First the test parameters are set. Then the test cycle begins. The cells are charged to full using a -dV algorithm to detect full charge. Then the cells are discharged at the test rate while timing the discharge. When a predetermined voltage is reached (0.9V) then discharge is terminated. Then the cells are charged again. At the end of test cycle the capacity measured during the discharge is displayed.

All cells are retail new and are run through 2 recondition cycle before capacity testing is performed. In all tests 4 cells are tested and results averaged. Please note that due to variations in manufacturing and testing any results within several percent of value should be considered identical for these tests. This chart will grow as I get more batteries to test. Enjoy the results.

Note; the BC-9009 and BC-1000 are identical except for the color of the case. Both have same circuit board revision and firmware revision. BC-9009 is no longer avaialble.

Batteries are ranked from results of the Battery Analyzer tests.

AA Cells

Battery Brand
and Type
Battery Analyzer
Discharged Capacity
Test Results
Test Results
Test Results
Test Results
Test Results
PowerEx AA 2700
2565 mAh 2420 mAh
2690 mAh
2610 mAh
2660 mAh
2451 mAh
Eneloop XX AA (LSD) 2475 mAh 2420 mAh 2510 mAh 2520 mAh 2610 mAh 2430 mAh
AccuPower AA 2900
2426 mAh 2359 mAh 2675 mAh 2522 mAh 2515 mAh 2447 mAh
Tenergy Premium AA 2500
2374 mAh 2367 mAh 2520 mAh 2457 mAh 2507 mAh 2365 mAh
Duracell AA 2550
2345 mAh 2340 mAh
2440 mAh
2390 mAh
2420 mAh
2275 mAh
PowerEx Imdeion AA 2400 (LSD) 2344 mAh 2210 mAh 2410 mAh 2290 mAh 2310 mAh 2254 mAh
Ansman AA 2850
2310 mAh
2286 mAh 2515 mAh 2407 mAh 2410 mAh 2375 mAh
TruCELL Precharged AA (LSD)
2310 mAh 2270 mAh 2400 mAh 2330 mAh 2320 mAh 2292 mAh
AccuPower AccuLoop AA 2300 (LSD)
2285 mAh 2235 mAh 2342 mAh 2240 mAh 2312 mAh 2268 mAh
Energizer Rechargeable AA 2300 (LSD)
2244 mAh 2220 mAh 2347 mAh 2292 mAh 2315 mAh 2191 mAh
Delkin Devices AA 2900 
2175 mAh 2192 mAh 2385 mAh 2330 mAh 2302 mAh 2197 mAh
La Crosse AA 2600 2130 mAh 2070 mAh 2460 mAh 2190 mAh 2150 mAh 2144 mAh
Amazon Basics AA 2000 (LSD)
2125 mAh 2112 mAh 2295 mAh 2237 mAh 2217 mAh 2151 mAh
Tenergy Centura AA 2000 (LSD)
2021 mAh 2008 mAh 2122 mAh 2085 mAh 2090 mAh 1946 mAh
Rayovac Platinum AA (LSD) 1997 mAh 2010 mAh 2090 mAh 2010 mAh 2100 mAh 1986 mAh
Eneloop AA White (LSD) 1975 mAh 1940 mAh 2100 Ah 2060 mAh 2110 mAh 1998 mAh
Tenergy (Blue) AA 2600
1970 mAh 1990 mAh
2140 mAh
2000 mAh
2040 mAh
1892 mAh
CFL AA 3800
642 mAh 639 mAh 672 mAh 677 mAh 666 mAh 641 mAh
BTY AA 3000
476 mAh
459 mAh
575 mAh
548 mAh
537 mAh
499 mAh
Ultrafire AA 3500
424 mAh
367 mAh
465 mAh
463 mAh
423 mAh
429 mAh

AAA Cells

Battery Brand
and Type
Battery Analyzer
Discharged Capacity
Test Results
Test Results
Test Results
Test Results
Test Results
AccuPower AAA 1200
988 mAh
1006 mAh
1007 mAh
1034 mAh
971 mAh
973 mAh
PowerEx AAA 1000 982 mAh 981 mAh 1026 mAh 984 mAh 1004 mAh 978 mAh
PowerEx Imedion AAA 950 (LSD) 927 mAh 907 mAh 1019 mAh 970 mAh 971 mAh 899 mAh
Duracell AAA 1000 919 mAh 934 mAh 1017 mAh 973 mAh 1026 mAh 918 mAh
Tenergy Premium AAA 1000
877 mAh 854 mAh 900 mAh 890 mAh 906 mAh 855 mAh
Amazon Basics AAA 800 (LSD)
824 mAh 834 mAh 903 mAh 899 mAh 897 mAh 833 mAh
Eneloop AAA White 800 (LSD) 799 mAh 832 mAh 877 mAh 827 mAh 835 mAh 835 mAh
AccuPower AccuLoop AAA 950 (LSD)
789 mAh
817 mAh
842 mAh
807 mAh
812 mAh
825 mAh
Tenergy Centura AAA 800 (LSD)
788 mAh 774 mAh 838 mAh 774 mAh 782 mAh 781 mAh
Rayovac Platinum AAA (LSD) 775 mAh 773 mAh 788 mAh 806 mAh 820 mAh 774 mAh
Tenergy (Blue) AAA 1000 750 mAh 760 mAh 811 mAh 779 mAh 808 mAh 751 mAh
La Crosse AAA 1000 741 mAh 789 mAh 842 mAh 835 mAh 799 mAh 775 mAh

Click on the above link to purchase on ebay.

(LSD) = Low Self Discharge type, ie. Imedion, Eneloop, AccuLoop
Four cells are tested on each charger.
The average of the four tested cells for each charger is displayed.

Test settings:
Maha MH-C9000.
Charge 1000 mA
Discharge 500 mA

La Crosse BC-700.
Charge 700 mA
Discharge 350 mA

AccuPower IQ328.
Charge 1000 mA
Discharge 500 mA

La Crosse BC-9009/BC-1000
Charge 1000 mA
Discharge 500 mA

Charge 1000 mA
Discharge 500 mA

Opus BT-C2000
Charge 1000 mA
Discharge 500 mA

C Cell

Battery Brand and Type
Battery Analyzer
500 mA rate
Battery Analyzer
1000 mA rate
500 mA rate
1000 mA rate
500 mA rate
Tenergy Premium C 5000
5268 mAh
5162 mAh
5136 mAh 5126 mAh 5296 mAh
AccuPower C 6000
5005 mAh
4950 mAh
5174 mAh 5126 mAh 4721 mAh
PowerEx Imedion C 5000 (LSD)
4231 mAh
4037 mAh
4050 mAh 3938 mAh 4166 mAh
Tenergy Centura C 4000 (LSD)
4172 mAh
3954 mAh
3996 mAh 3848 mAh 4054 mAh
PowerEx C 5000
4049 mAh
3895 mAh
4372 mAh 4156 mAh 4236 mAh
AccuLoop C 4500 (LSD)
3890 mAh
3870 mAh
4044 mAh 3888 mAh 3996 mAh

D Cell

Battery Brand and Type
Battery Analyzer
500 mA rate
Battery Analyzer
1000 mA rate
500 mA rate
1000 mA rate
500 mA rate
AccuPower D 11500
 10088 mAh
9882 mAh
10290 mAh 10020 mAh 10290 mAh
Tenergy Premium D 10000
9944 mAh
9544  mAh
8952 mAh 8138 mAh 10130 mAh
PowerEx Imedion D 9500 (LSD)
8690 mAh
8549 mAh
8338 mAh 8187 mAh 8714 mAh
AccuLoop D 10000 (LSD)
8192 mAh
8298 mAh
8324 mAh 8338 mAh 8440 mAh
Tenergy Centura D 8000 (LSD)
8170 mAh
8044 mAh
8440 mAh 8282 mAh 8246 mAh

Internal resistance measurement.

Batteries can be modeled as a voltage source in series with a resistance. In practical terms internal resistance gives an indication of how well a battery can supply current to a load without the cell voltage dropping. Low internal resistance means low cell voltage drop under load. High internal resistance means high cell voltage drop under load. So if you are looking for a battery that can delivery high current to the load you want a battery with low internal resistance. In this test internal resistance is measured using the DC method. A programmable current source is used as the load so that load current can be precisely controlled. Cell voltage is measured by a high accuracy bench DVM. The results give a change in cell voltage for each current load. This data is plugged into ohms law to calculate the equivalent resistance. Internal resistance in the chart below is given in mili-ohms, that is thousandths of an ohm. Lower is better.

AA Cells

Battery Brand
and Type
Internal Resistance Average
Test Current 500mA
Test Current 1000mA
Test Current 2000mA
Duracell AA 2550 46 mΩ 46 mΩ 45 mΩ 48 mΩ
Eneloop XX AA (LSD) 47 mΩ
50 mΩ 44 mΩ 48 mΩ
Energizer Rechargeable AA 2300 (LSD) 48 mΩ 52 mΩ 41 mΩ 52 mΩ
Eneloop AA White (LSD) 50 mΩ 52 mΩ 48 mΩ 49 mΩ
PowerEx AA 2700 55 mΩ 68 mΩ 49 mΩ 48 mΩ
AccuPower AccuLoop AA 2300 (LSD) 56 mΩ 64 mΩ 52 mΩ 53 mΩ
Tenergy Centura AA 2000 (LSD) 60 mΩ 66 mΩ 56 mΩ 58 mΩ
PowerEx Imdeion AA 2400 (LSD) 62 mΩ 50 mΩ 69 mΩ 66 mΩ
Tenergy Premium AA 2500 62 mΩ 68 mΩ 60 mΩ 57 mΩ
Tenergy (Blue) AA 2600 66 mΩ 56 mΩ 73 mΩ 69 mΩ
truCELL Precharged AA (LSD) 68 mΩ 78 mΩ 65 mΩ 61 mΩ
AccuPower AA 2900 71 mΩ 72 mΩ 69 mΩ 71 mΩ
La Crosse AA 2600 74 mΩ 90 mΩ 68 mΩ 63 mΩ
Amazon Basics AA 2000 (LSD) 81 mΩ 82 mΩ 94 mΩ 68 mΩ
Rayovac Platinum AA (LSD) 86 mΩ 82 mΩ 87 mΩ 90 mΩ
Delkin Devices AA 2900
97 mΩ 98 mΩ 94 mΩ 100 mΩ
Ansman AA 2850
105 mΩ 98 mΩ 111 mΩ 106 mΩ
CFL AA 3800
115 mΩ 125 mΩ 110 mΩ 109 mΩ
BTY AA 3000
119 mΩ 140 mΩ 114 mΩ 105 mΩ
Ultrafire AA 3500
139 mΩ 152 mΩ 132 mΩ 133 mΩ

AAA Cells

AccuPower AAA 1200 71 mΩ 72 mΩ 69 mΩ 71 mΩ
Duracell AAA 1000 84 mΩ 80 mΩ 87 mΩ 84 mΩ
PowerEx AAA 1000 86 mΩ 80 mΩ 98 mΩ 81 mΩ
Tenergy Premium AAA 1000 86 mΩ 88 mΩ 87 mΩ 84 mΩ
PowerEx Imedion AAA 950 (LSD) 96 mΩ 108 mΩ 87 mΩ 92 mΩ
Eneloop AAA White (LSD) 96 mΩ 98 mΩ 101 mΩ 90 mΩ
Rayovac Platinum AAA (LSD) 98 mΩ 99 mΩ 102 mΩ 94 mΩ
Tenergy (Blue) AAA 1000 104 mΩ 104 mΩ 115 mΩ 92 mΩ
AccuPower AccuLoop AAA 950 (LSD) 113 mΩ 106 mΩ 126 mΩ 106 mΩ
Tenergy Centura AAA 800 (LSD) 113 mΩ 122 mΩ 113 mΩ 103 mΩ
Amazon Basics AAA 800 (LSD) 126 mΩ 124 mΩ 111 mΩ 143 mΩ
La Crosse AAA 1000 141 mΩ 152 mΩ 140 mΩ 131 mΩ

C Cells

Battery Brand and Type
500 mA
1000 mA
2000 mA
3000 mA
Tenergy Premium C 5000 18 mΩ 18 mΩ 18 mΩ 18 mΩ 19 mΩ
Tenergy Centura C 4000 (LSD) 24 mΩ 34 mΩ 13 mΩ 24 mΩ 24 mΩ
AccuLoop C 4500 (LSD)
25 mΩ 24 mΩ 26 mΩ 26 mΩ 23 mΩ
AccuPower C AP6000
27 mΩ 32 mΩ 28 mΩ 25 mΩ 24 mΩ
PowerEx C 5000
28 mΩ 20 mΩ 42 mΩ 27 mΩ 26 mΩ
PowerEx Imedion C 5000 (LSD)
55 mΩ 80 mΩ 40 mΩ 42 mΩ 60 mΩ

D Cells

Tenergy Centura D 8000 (LSD) 15 mΩ 12 mΩ 14 mΩ 15 mΩ 17 mΩ
Tenergy Premium D 10000
17 mΩ 20 mΩ 15 mΩ 16 mΩ 16 mΩ
AccuLoop D 10000 (LSD) 19 mΩ 30 mΩ 15 mΩ 16 mΩ 15 mΩ
AccuPower D 11500
20 mΩ 28 mΩ 14 mΩ 22 mΩ 16 mΩ
PowerEx Imedion D 9500 (LSD)
33 mΩ 44 mΩ 28 mΩ 25 mΩ 37 mΩ

So what does it mean??
Example: If the internal resistance is 50 mΩ and you need to drive a load of 1 A and assume a no load cell voltage of 1.25V then under that load cell voltage would drop to 1.20V.
If you need to drive a 2A load then the cell voltage would drop to 1.15V.
If the internal resistance is 100 mΩ at 1A load then cell voltage would drop to 1.15V. Under 2A load it would drop to 1.05V.

Of course the C and D cells performed the best.
All of the AA batteries seem to range form fair to good in terms of internal resistance.
The AAA batteries did not test as well but of course they have far less electrode surface area. However most put up a respectable performance.

Note: Only the BT-C2000 and BM200 charger has internal resistance measurement function.