Battery powered, or cordless grass trimmers, have a number of advantages over conventional gas trimmers. They are lighter, quieter and cleaner than gas powered trimmers and require less maintenance. They can also go places corded electric trimmers can't. Along with these advantages, however, come a number of trade-offs that make battery powered trimmers less well suited for large or densely overgrown lawns.
Battery powered trimmers are the least powerful type. They provide substantially less power than gas trimmers and are even weak compared to the underpowered corded trimmers. According to American Lawns, they will not clear "brush, tall grass, or weeds," so they are only really well suited to well-maintained lawns without weed problems or debris.
Short Battery Life
Unlike corded trimmers, battery-powered lawn trimmers allow you to go everywhere without dragging an extension cord, but there is a payoff for that convenience. Battery powered lawn trimmers generally have between 20 and 40 minutes of power, which is not enough time to trim large lawns or landscapes which require a lot of edging. Keeping an extra battery charged can double the time available, but you still must stop and change batteries in the middle of the job.
Like corded trimmers, battery powered trimmers are not safe to use in the rain. If water gets into the battery or motor compartment it can cause a short, damaging the trimmer or potentially injuring the user. Gas trimmers, on the other hand, are safe to operate in the rain.
Battery powered trimmers take time to charge. Depending on the type of battery used, the trimmer may take over one hour to charge. Over time, electrical batteries leak out their charge, which means that if you charge up your trimmer after use, it may not have its full energy in a week when you trim your lawn next. Leave the battery plugged in to a trickle charger, or give it a short charge before starting to top it off. Battery powered lawn trimmers require less maintenance than gas trimmers, which may balance out the inconvenience of charging the batteries.