Myoguide Power: Alkaline Versus NiMH Rechargeable Batteries
Even though the NiMH rechargeable batteries have a lower specified capacity (2300mAH) and lower voltage (1.2V) compared to a typical Duracell ProCell Alkaline AA battery (2850mAH, 1.5V), they tend to provide more capacity in a higher current draw situation. The following article covers Myoguide Battery Strategies to get the longest battery life.
NiMH rechargeable batteries provide a steadier discharge than an alkaline battery. i.e. Alkaline batteries have a steeper discharge curve as the load current requirements increase.
The downside to using a NiMH rechargeable in the Myoguide is that the battery display icon is calibrated for a 1.5V (Alkaline) battery and hence when using NiMH rechargeables, the battery icon will only display ¾ full when the NiMH are at full charge and will show empty when batteries are 50% discharged. i.e. The unit will run for quite a considerable time when the battery icon shows empty.
Note: Due to the fact that battery discharge is not linear, but rather is logarithmic. The battery detection circuit is designed to linearly display the current battery voltage; hence, the display is not a truly accurate rendition of the state of charge. i.e. when the display shows one bar, there still may be considerable battery capacity remaining. The batteries should be replaced when the display indicates “ Battery Low!”. This is one of the best Myoguide Battery Strategies.
Battery Test Comparison
Test 1:
80% EMG mode with 200Hz, 1mVp-p signal in, Vol:4. 20% Stimulation @ 1mA, 500uS pulse width, 1 Hz frequency into a 10 KΩ load
Alkaline batteries (Duracell MN1500): 8 Hr. 20 min.
Alkaline batteries (Duracell ProCell PC1500): 8 Hr. 10 min.
NiMH Rechargeable (Energizer NH15): 14 Hr. 39 min.
Test 2:
Constant Stimulation @ 4mA, 500uS pulse width, 1 Hz frequency into a 10 KΩ load
Alkaline batteries (Duracell MN1500): 3 Hr. 5 min.
Alkaline batteries (Duracell ProCell PC1500): 2 Hr. 15 min
NiMH Rechargeable (Energizer NH15): 4 Hr. 35 min
Test 3:
Constant Stimulation @ 1mA, 500uS pulse width, 1 Hz frequency into a 10 KΩ load
Alkaline batteries (Duracell MN1500): 3 Hr. 33 min
Alkaline batteries (Duracell ProCell PC1500): 3 Hr. 6 min
NiMH Rechargeable (Energizer NH15): 5 Hr. 17 min
Test 4:
80% EMG mode with 200Hz, 1mVp-p signal in, Vol:4.
20% Stimulation @ 4mA, 500uS pulse width, 1 Hz frequency into a 10 KΩ load
Alkaline batteries (Duracell MN1500): 7 Hr. 47 min.
Alkaline batteries (Duracell ProCell PC1500): 7 Hr. 35min.
NiMH Rechargeable (Energizer NH15): 9 Hr. 33 min.
Conclusion:
NiMh rechargeable battery use in the Myoguide unit provides considerably more run time compared to disposable alkaline batteries. This is especially true when the unit heavily used in Stimulation Mode.
NiMH Rechargeable Batteries have the longest Myoguide battery life!
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