The one I have charges from 110V. When it charges fully, it goes into “trickle mode”, meaning it only does maintenance charging. Safe to keep plugged in all the time.
I leave it in my vehicle, hooked up to a 110V 400 watt inverter that only runs when my vehicle is started. According to the built in power meter, it has never fallen below a full charge since I started doing this.
I use it when camping to recharge cell phones, run lights, etc., and of course, if there’s an emergency, to start my vehicle. I can also take the inverter and plug it into the jump starter and run my netbook for about 9 hours or so.
Similar to this: http://www.batterychargers.com/ProductDetail.aspx?ProductName=94026904
That one is 18Ah. The more Ah (amp hours) the longer you can run it on a charge. I’ve seen them well above 25 in places, but obviously, the more amp hours, the more expensive.
Lots of good ones here: http://www.batterychargers.com/CategoryDetail.aspx?CategoryName=Jump-Starter-%2F-Portable-Power_Emergency-%2F-Recreational
thanks. will check it out.