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A DC to AC "inverter" simply takes the 12V DC (Direct Current, such as is delivered from batteries such as your car/vehicle batteries) from your car, and coverts DC to AC (Alternating Current, such as you find in your household electrical outlets). After market inverters are going to be powered typically from a cigarette lighter port or a dedicated 12V DC port found in some newer vehicles, and via electronics they produce 100 - 120V AC.
A small 200 - 300 watt unit would be more than sufficient for powering your MH-25 charger and probably would be sufficient for pretty much anything you ever plan on charging.
But to be sure before buying - you should first be aware of how much power your device(s) requires so you don't overtax the inverter or buy too small an inverter. While they'll have safety mechanisms (breakers and other over-current protection) it's still best to do the research first.
For example a 300 watt inverter won't power a 1000 watt hair dryer, or won't for very long.
Usually a charger or other device will list the input power requirement in Watts; if they don't, you should be able to calculate input power required assuming they've listed (as they must) the input voltage and current requirement for the device.
Perfect example: Your MH-25 charger for EN-EL15 packs requires input voltage of 120V and draws 0.2 amps of current.
Power is calculated as Volts (times) Amps so 120V * 0.2A = 24 Watts.
Clearly a 200W inverter would handle that load with ease. You'll find that any lithium ion cell/pack charger where the "packs" are just one or two cells will require quite low power (watts) - so your USB style phone chargers, most or call camera chargers, toy chargers and such should all fall well under 100 watts input power requirements. Laptop chargers will typically require between 70 - 100W of power, and again that's a load which a 200W inverter can easily handle.
As cell counts go up -- laptops are great examples here -- the charging power requirement typically goes up. My laptop charger specifies 90W. The inverter built into our Ford F-150 is rated to 150W - it really is designed for charging devices like phones and cameras and laptops rather than powering Margarita Makers and Hair Dryers or large air compressors.
To avoid draining the vehicle's main battery, the built in inverter in our vehicle times out after 13 minutes of use when the vehicle is shut off. If your 12V outlet / cigarette lighter port doesn't power down when the vehicle is off, be careful not to leave your inverter powered up.
If you buy a decent inverter it should last many, many, years. Don't buy a huge 1000W inverter for this purpose, unless you have other needs... and if you do buy a big unit you should get it professionally installed as they need to be wired directly to your vehicle's electrical system, are typically mounted under the hood (or in the bed of a truck) and the installation needs to be done properly to ensure safety (proper gauge cables that are fused right at the point of power interface with your car to protect against shorts, etc).
The smaller units which plug in to the 12V system via a cig lighter are user installable of course.
Edited on Feb 01, 2013 at 05:18 PM · View previous versions