M4 Battery Backpack Sprayer Review: 4.5 Gallon, 20 to 80 PSI

The M4 is best at long spraying sessions where hand pumping becomes the limiting factor: spot-treating weeds across a big yard, fence lines, gravel drives and beds, or applying liquid fertilizer to a smaller lawn.

• No pumping. A 12V pump keeps pressure steady, so output does not fade as you walk the way a manual sprayer's does between strokes.
• Adjustable pressure. The rotary dial sets 20 to 80 psi. Lower pressure makes coarser droplets that drift less, which many herbicide labels call for.
• Reach. A stainless wand that extends from 24 to 48 inches reaches under shrubs and along fences, and a second plastic wand resists harsh chemicals.
• Nozzle choice. Brass fan tips for even broadcast bands, cone nozzles for spot treatment and shower nozzles for gentle watering-in.
• Capacity. 4.5 gallons is more than the common 4 gallon manual backpacks such as the Chapin 61800 ProSeries 4-Gallon Backpack Sprayer.

The biggest drawback is weight. Water weighs about 8.34 lb per gallon, so a full 4.5 gallon tank is about 37.5 lb of liquid before you add the sprayer body and a sealed lead-acid battery, which is much heavier than a lithium pack of similar capacity. Expect a loaded weight well over 40 lb. For many users, especially on slopes, filling it halfway is the practical choice.

The second drawback is the battery chemistry and missing figures. Sealed lead-acid batteries lose capacity if stored discharged, so keep it charged over winter as the manual directs. The listing does not state runtime per charge or a warranty term, and the valve handle is plastic. Owners who spray an acre or more will spend more time refilling than spraying; a tow sprayer suits that job better.

These themes summarize published owner reviews of the M4 battery backpack sprayer, not our own use.

Praise themes

• No more pumping, so long sessions are far less tiring.
• Steady pressure and a consistent spray pattern.
• The adjustable wand and nozzle assortment cover most jobs.
• Battery charge lasts through typical homeowner sessions.

Complaint themes

• Heavy when full, and the lead-acid battery adds weight.
• Some owners report leaks at fittings or the lid that need tightening.
• Plastic parts, such as the valve handle, feel less durable than the brass nozzles.
• Battery life declines if the sprayer is stored uncharged.

Buy it if

• You spray for long sessions and hand pumping tires you out.
• You spot-treat weeds across a large property, or treat lawns up to roughly 10,000 to 20,000 square feet with liquids.
• You want pressure control to follow label drift directions.
• You can comfortably carry 40 lb or more, or will fill partway.

Skip it if

• You spray small areas occasionally; the Smith Performance Sprayers R200 2-Gallon Compression Sprayer is a pro handheld.
• You want a cheaper, lighter manual backpack; the Solo 425 4-Gallon Piston Backpack Sprayer reaches 90 psi with a piston pump.
• You broadcast-spray an acre or more; the Agri-Fab 15 Gallon Tow-Behind Lawn Sprayer with Boom tows a boom behind a tractor.
• Carrying a heavy load on your back is not advisable for you.

Liquid lawn products list a spray volume, often in gallons of mix per 1,000 square feet. Divide 4.5 gallons by that volume to get coverage per tank; always use your label's volume and rate.

Warranty: the listing does not state a warranty term. Ask My4Sons about coverage for the pump, battery and charger before buying, and keep your receipt.

Certification: the listing does not state a UL, ETL or CSA listing for the charger; check its label for a safety certification mark, and charge the battery in a dry, ventilated area away from the chemicals you spray. Sprayers themselves are not pesticide-registered products: the EPA-registered label on the herbicide or insecticide governs how you apply it.

Recalls: we cannot query the recall database for you, so check the CPSC recall database at cpsc.gov/Recalls for this model and its serial range before you buy, and again once a year after you own it. Register the product with the manufacturer so a recall notice reaches you directly.