Did you know you can leverage your power tool batteries to power other items?
I have several Ridgid brand power tool battery packs. They are available with the same interface yet varying capacities from 2Ah to 8Ah on the high end.
In my experience these battery packs are durable, lightweight, and fast charging. I had long wondered about using these battery packs for things other than Ridgid power tools, since it seemed a waste having them sitting around waiting for the next job.
As it turns out, this is easily done by using a DC to DC power supply, or "buck converter", and an appropriate adapter for your power tool batteries. This device will take an input voltage, and step it down to a desired output voltage. So for example, the Ridgid batteries are 18V. If I want 10V DC to power a Baofeng UV-5R charger, I select 10V output on the DC power supply. Connect the battery, and apply the power. Mission accomplished.
Some ideas for these are powering an inverter to get AC output, power laptops, powering battery chargers, DC fans, etc. The goal isn't necessarily efficiency, but flexibility. That said, many electronic devices are DC, so this can bypass the DC→AC→DC conversion and associated efficiency loss that is happening whenever you see a wall-wart.
To get a decent estimate of battery runtime, we'll need to convert your battery's capacity from amp-hours (Ah) to watt-hours (Wh). Taking the example of a 4Ah 18V Ridgid battery, I would use the following formula:
(4Ah × 18V) = 72Wh capacity
(72Wh ÷ 20W) = 3.6 hours runtime
I did a considerable amount of research an settled on Riden branded DC power supply kits out of China. They are well designed, well priced for my needs, and highly capable. In this instance I purchased the DPS5020 kit which is capable of 50V 20A DC output. While I haven't run the DPS anywhere near maximum capacity, it has been excellent recharging batteries, powering radio equipment, and powering small inverters to convert to AC power.
I found the kits simple to assemble. The only deviations I made were using lower gauge wiring internally (I highly recommend using silicon wire for flexibility--I used wiring from Home Depot which was over-kill and made it more difficult for myself trying to bend and solder the wire in the confined spaces of the cases). You'll need a decent soldering iron, and I highly recommend a good meter for testing your work prior to throwing any switches.