I like to buy a battery charger "by the pound"- - - - -there's no substitute for a big transformer and a good rectifier. The little portable chargers are OK for occasional use or topping off a low battery occasionally, but if you want to actually have one that can boost a dead vehicle or be used frequently, bite the bullet and get one with a full-sized cabinet and some wheels, and at least a 100 amp boost capability.
Jerry

"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway
Love your enemies and drive 'em nuts!