OK, a car charger with a trickle charge feature, can actually have a battery go "flat" while connected to it and switched on. The volatage may stay up, but the total amp hrs can decrease.
Next problem. A car charger with trickle charge, will never take a battery to it's full current capacity.
A "smart" charger works this way. It first has a bulk charge. This is just like the main charge feature of a standard car charger. The next stage is "Absorbtion". This is where the shortfall occurs with a car charger and even Multi stage chargers can have variances as to how they achieve this. Absorbtion is a much higher voltage, but very low current. It allows the battery to absorb it's full capacity of charge. Once this has happend, then the multi stage charger will go into a float stage. This is similar to trickle charging BUT. This is where many differences occur in makes and models and namely price
. The more expensive charger can even have temperature monitoring for charge acceptance and trickle maintanance.
There are also some four stage chargers available now. The first stage is monitoring stage that checks the battery conditon before a "customised" charge cycle is started.
On good batteries, a multi stage charger can make a bank perform better and longer than a standard car charger ever will. But the draw back is just like what I went through recently. The batteries are getting toward the end of their life and would not accept a full charge anymore. The result is that the batteries boiled. Not a fault as such of the charger. If I had temperature monitoring (couldn't afford that one) then I wouldn't have had a problem.
And finally, there are good chargers and bad charger out there. It just comes down to what you want to pay. But a smart charger will be more benificial to the house banks perfomance and longevity than a standard car charger anyday.