Charging Cordless Tools with your Vehicle

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Spanish Truck batteries, deep-cycle backup batteries, power inverters, and cordless tools — what's the deal? May 6, 2007

Question
I am always trying to reduce the number of tools I carry into a house. I am thinking about leaving my battery chargers in my van hooked up to a power inverter. Will this drain my battery in my van? If not, what size inverter would it take to run 3 or 4 battery chargers?

Forum Responses
(Cabinet and Millwork Installation Forum)
From contributor A:
That will suck your batteries dry faster than you can say Linda Lovelace. You would have to keep the van running, and at $3.35 a gallon, I'm not idling to charge cordless; if you want a motor running, add a gas powered generator. Just run an extension cord to a power strip in the van. I wouldn't mess with an inverter.

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From contributor B:
If you have the right setup you won’t suck your battery dry. However, most inverters put out a modified square wave instead of a true sine wave. This will damage most batteries because of the way the chargers work. Most modern chargers are transformer-less and they rely on the sine-wave being true. If you hook up a charger to an inverter that has a modified square-wave output, your tools’ battery life will be shortened considerably. I have a Vector 3000 watt inverter that I use to power most if not all of my tools. I have a separate deep cycle battery to operate it from. I have a boat battery switch to keep it isolated, or in parallel with my car battery or to operate the inverter from just the car battery/alternator. This way I have a choice from which source my battery drain will come from. With the one deep cycle battery and normal tool usage I can average about an 8 hour day before the battery starts to show itself weakened. This does not include my tablesaw or my 1HP compressor, which draw a lot of current. If I run low on battery power at the end of the day I can run the car battery and the inverter battery in parallel to extend the use. I can also run the engine and operate off of the alternator. But this uses expensive fuel and I try to avoid it.

You can get a true sine-wave inverter, but they a 2 to 3 times more expensive to buy. They usually don't have the surge capabilities that the modified square-wave units have. If you are only planning on using it to charge your batteries then I think you could spend your money better elsewhere. Have you looked into a 12 v charger for your batteries, made specifically for your battery? They should exist, at least in a 3rd party vendor.