Jumper Battery Pack for 12-volt Vehicles

<...totally useless on a totally dead battery.It requires a certain amount of voltage from the battery to engage the start or boost logic....>

All it is doing is trying to protect itself from the unwanted effects of overcurrent. A <...dead battery...> can look like a short circuit.

The old "Dumb" chargers had a circuit breaker for short circuit protection,as well as a TCO in the transformer to prevent overheating.

TCO - Definition by AcronymFinder

In this case,it is a Thermal Cut Out,or Cut Off device that will open when above a certain temperature.Examples are Klixon.Some reset automatically,some manually,and some are not re-settable.They are practically everywhere;"Coffee pots,toasters,etc.

Some are embedded within the transformer windings and not easily accessible.

Why one would entertain the purchase of a <...smart charger...> is the question, then.

I bought one. Harbor Freight.

I have a dodge Tacoma truck, a board had shorted out behind the dash where it constantly drained if not used enough. The board itself was $250, the labor to just install it was like $1500.

I use it as a work truck so to speak, everything is good on it… when I’m at my rental property’s, at times, I’m in the middle of the lawn, which is about 5 acres. The dam thing dies. No other vehicle for a jump start.

Sure I got AAA, but I don’t have time for that, instead, I take it out at give it a jump.

so that’s one reason.

Ah! So.

I would not buy one now for the emergency situation,and I may not ever need it again,but then,I carry a spare tire just in case.

I have helped several others with weak batteries so it is not a total loss.

You shouldn't let your batteries go dead in the first place...I only connect the battery when I'm going to use the car, otherwise the battery is disconnected...and don't leave your car in the airport parking lot(too many thieves about), Uber to airport and back...

A lead acid battery will sulfate and go dead even when no load is connected if it sits for a while without a maintenance charge.

When I buy a new battery,I look at the manufacture date first.Some have been on the shelf a long time, slowly dying.

All batteries used to be stored dry,and acid was added when purchased.They only do that now with some motorcycle batteries.

I will top the charge off after one month of sitting, but it doesn't take much...You need to drive your car once in a while just to keep it in good working order anyway...I think the maximum time sitting is about six months for battery preservation, but I wouldn't recommend letting your car sit more than about 2 months max......minimum resting voltage should be 12.5 volts...If it drops below that, then it needs to be topped...mine usually tops out around 12.7...

I have replaced many a selenium bridge rectifier with a 40 Amp silicon or shottke bridge rectifier, they are dirt cheap but you need to remove some secondary windings else the charger will supply too high a voltage to the battery.

A bridge will have upto a 1.2volt forward voltage drop depending on the type of diodes used and the bridges have a rating above 400volts where as the selenium rectifier has around 1volt per plate and a reverse voltage max of 25volts.

These newer type chargers are just too damn smart to work with flat batteries where as a current limited grunt charger does the trick.

I too have replaced many selenium rectifiers with silicon diodes.

I replaced a bridge selenium with a full wave bridge,and built a voltage regulator to harness the extra voltage and current.

Thanks.

I have a small Canadian made "smart" charger I use for my Lead/acid batteries that works great to revive a dead battery.

I also have a small solar panel on the dash of the the cars that park for a week or more between trips. Keeps the battery happy the whole time. I run the wires from the dash and into the battery compartment where it's wired in permanently.