iStim EV-804 Rechargeable TENS/EMS Combo Unit — 2 Channels, 24 Programs

The iStim EV-804 is a rechargeable, dual-channel electrotherapy device combining TENS sensory stimulation and EMS muscle stimulation in one portable unit.

Use the TENS programs when the goal is strong but comfortable sensory stimulation for temporary pain management support. Select EMS when the goal is a controlled muscle contraction using adjustable ramp, contraction, and relaxation settings.

The EV-804 includes:

• Two independently controlled output channels
• Five TENS modes
• Two EMS modes
• 24 manufacturer-listed programs
• Adjustable pulse rate and pulse width
• Adjustable EMS ramp, contraction, and relaxation timing
• A backlit LCD screen
• Rechargeable lithium-battery power
• Eight reusable 2 × 2-inch electrode pads
• Two lead-wire sets
• USB charging accessories

The EV-804 is manufactured in Taiwan and is FDA 510(k) cleared for over-the-counter TENS and EMS use.

• Rechargeable TENS and EMS combination unit
• Two independent channels
• Supports one or two electrode-pair placements
• Five adjustable TENS modes
• Two adjustable EMS modes
• 24 manufacturer-listed programs
• Separate intensity dial for each channel
• Adjustable pulse rate from 2–150 Hz
• Adjustable pulse width from 50–300 microseconds
• EMS ramp adjustable from 1–8 seconds
• EMS contraction time adjustable from 2–90 seconds
• EMS relaxation time adjustable from 0–90 seconds
• Treatment timer up to 60 minutes
• Backlit digital display
• Eight reusable electrodes included
• Rechargeable lithium-battery design
• USB charging set included
• OTC Class II medical device
• Made in Taiwan

The manual for the EV-804 control platform lists the parameter ranges above. Because the EV-804 has existed in both disposable-battery and lithium-battery configurations.

TENS and EMS both deliver electrical pulses through skin electrodes, but they are intended to produce different responses.

Read TENS vs. NMES: Differences, Uses, and Device Selection for a complete explanation.

The EV-804 provides five established TENS stimulation patterns.

The TENS modes are intended to provide different sensory experiences. No single mode is automatically best for every person, body area, or treatment goal.

For additional guidance, read What the Five TENS Modes Are Used For.

The EV-804 adds two contraction-based muscle-stimulation modes.

In alternate mode, the technical instructions state that Channel 2 begins after the Channel 1 contraction is completed. The manual also specifies that the relaxation time should be at least as long as the contraction time in this mode.

A true EMS program needs more than intensity. The EV-804 allows the user or clinician to define how each contraction begins, how long it lasts, and how long the muscle rests.

The contraction time must be long enough to include both the ramp-up and ramp-down periods. NMES and EMS settings should be selected according to the target muscle, treatment goal, fatigue level, and professional instructions.

Each EV-804 channel has its own intensity control.

That allows the user to:

• Use one electrode pair on a focused area
• Use both channels with four electrodes
• Set different intensity levels on the right and left sides
• Surround a larger area with two electrode pairs
• Stimulate two related muscles
• Use synchronous or alternating muscle contractions

The channels do not need to be set at identical intensity levels. Skin resistance, electrode condition, pad position, body contour, and individual sensitivity can cause one channel to feel stronger than the other.

The current EV-804 is a rechargeable version supplied with USB charging accessories. FDA cleared the EV-804 as a lithium-battery-powered OTC TENS/EMS

The EV-804 is rechargeable, but not wireless. Lead wires are still required between the device and electrode pads.

Do not operate the device while it is connected to charging equipment unless the current included manual explicitly permits it.

The included 2 × 2-inch electrodes are a general-purpose size. Other compatible sizes may be useful for different body areas.

Larger electrodes spread current across a broader surface. Smaller electrodes concentrate the current over less skin and may feel stronger at the same device setting.

1. Charge the device

Charge the unit using the supplied cable and charger before the initial session.

2. Turn both channel controls off

Rotate both intensity dials fully down before connecting the lead wires or applying the electrodes.

3. Connect the lead wires

Insert the lead wires securely into the Channel 1 and Channel 2 output ports.

4. Attach the electrodes

Connect each pad to the lead-wire pin before placing it on the skin.

5. Prepare the skin

Apply the electrodes to clean, dry, intact skin. Remove lotion, oil, perspiration, and dirt that could reduce adhesion or create uneven stimulation.

6. Position the electrodes

For TENS, pads are generally placed around or near the intended treatment area.

For EMS, pads are generally positioned over the muscle belly and motor-point region so that stimulation produces the desired contraction.

7. Select TENS or EMS

Choose the modality and program that match the intended goal.

8. Adjust the available parameters

Depending on the selected mode, adjust the following:

• Pulse rate
• Pulse width
• Ramp time
• On time
• Off time
• Treatment timer

9. Increase each channel gradually

Raise Channel 1 until the stimulation reaches the desired comfortable level. Repeat for Channel 2 when it is being used.

10. Monitor the session

Reduce or stop stimulation for sharpness, burning, pain, an uncontrolled contraction, or worsening symptoms.

11. Turn intensity down before removing pads

Return both channel controls to zero and switch the device off before disconnecting or removing the electrodes.

TENS generally produces the following:

• Tingling
• Tapping
• Buzzing
• Rhythmic pulsing
• A changing sensation during modulation modes

The intensity should be strong and clearly noticeable but comfortable. Conventional TENS usually should not produce a forceful muscle contraction.

EMS normally begins with tingling and increases until the target muscle contracts.

A properly adjusted EMS cycle may feel like

1. Stimulation rises gradually during the ramp.
2. The target muscle tightens.
3. The contraction remains active for the selected time.
4. The output declines.
5. The muscle rests during the off time.
6. The cycle repeats.

The contraction should be controlled and tolerable. It should not feel sharp, burning, or painful.

Dedicated units may be simpler when only one modality is used at a time. The EV-804 reduces the number of devices and power systems required.

The EV-804 may be a good fit for buyers who want the following:

• TENS and EMS in one device
• Rechargeable battery power
• Two independently controlled channels
• Familiar Burst, Normal, Modulation, SD1, and SD2 TENS modes
• Synchronous and alternating muscle stimulation
• Adjustable EMS ramp and work-rest cycles
• Eight starter electrodes
• A backlit display
• Manual control over pulse rate and pulse width
• An over-the-counter electrotherapy device
• A unit made by an established Taiwanese medical-device manufacturer

• Only TENS is required.
• Only NMES or EMS is required.
• Four independent channels are needed.
• Interferential or Russian stimulation is required.
• Compliance tracking is essential.
• Body-part presets are preferred.
• A lead-wire-free wearable device is required.
• Professional ultrasound or clinic-based electrotherapy is needed.

Browse our complete TENS collection, neuromuscular stimulation devices, and electrotherapy electrodes.

FDA cleared the lithium-powered EV-804 as an OTC TENS/EMS combination device.

The TENS function is intended for temporary relief of pain associated with sore and aching muscles in the following:

• The low back
• The arms
• The legs

The cleared labeling ties these symptoms to strain from exercise or normal household and work activities.

The EMS function is intended to stimulate healthy muscles to improve or facilitate muscle performance.

The product page should not claim that the EV-804:

• Cures chronic pain
• Treats arthritis itself
• Heals injuries
• Repairs damaged muscles
• Prevents blood clots
• Reverses nerve damage
• Replaces physical therapy
• Produces permanent pain relief

Do not use the EV-804 with a pacemaker, implanted defibrillator, or other implanted electronic device unless specifically cleared by the appropriate physician and device manufacturer.

Do not place electrodes:

• Across the chest
• Through the head
• Over the eyes or mouth
• On the front or sides of the neck
• Over the carotid sinus
• Over open wounds or broken skin
• Over infected or significantly irritated skin
• In another location prohibited by the instruction manual

Obtain medical guidance before use in the presence of:

• Pregnancy
• Epilepsy
• Heart disease
• Recent surgery
• Impaired sensation
• Poor circulation
• Undiagnosed or changing pain
• Another significant medical condition

Do not use electrical stimulation while driving, operating machinery, bathing, or performing an activity in which an unexpected sensation or muscle contraction could cause injury.

The iStim EV-804 Rechargeable TENS/EMS Combination Unit is a practical choice for users who need both:

• Sensory-level TENS stimulation
• Contraction-based EMS muscle stimulation

Its main advantages are the following:

• Two independent channels
• Seven stimulation modes
• 24 manufacturer-listed programs
• Rechargeable lithium-battery power
• Adjustable TENS and EMS parameters
• A backlit display
• Eight included electrode pads
• USB charging
• FDA 510(k)-cleared OTC status