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MAKE Flickr photo pool member NJfourwheeler fixed and modded a weed wacker he found – “A few weeks ago I trash picked a rechargeable weed whacker complete with charger. At first the charger wouldn’t report a full charge and battery life was extremely short. I assumed this is why the unit was out in the trash. After 4 or 5 complete discharge and charge cycles the battery started coming back to life and the charger is now giving the green light for a full charge. I can get about 10 to 15 minutes of good whacking with the on board battery, but that’s just not enough for my 3/4 acre yard. I solved the problem with a simple automotive relay, an RC car replacement power connector and one of two sealed lead-acid batteries that I have been keeping on a battery tender for the good part of 5 or 6 years. The NC connection on the relay provides power from the on board battery when used without the external source. When the coil is energized by the outboard battery the NO connection is closed and power is then supplied by that outboard power source. I whacked my yard for a good half hour of non stop thrashing without any noticeable decrease in power or speed. I didn’t take any pictures until it was done and back together, but trust me, there’s a relay inside there. I also removed the ridiculous trigger safety mechanism. C’mon now Black and Decker, it’s a 12 volt weed whacker not a table saw for Christ’s sake. Oh yeah and all of this cost me zero dollars…”Link.