Automobile battery charger, marine batteries

[Weyalan]

So, while I save up for a wind generator and / or solar panels, I need to keep my batteries charged. At the moment, I am not running the motor all that much, so I want to be able to charge the batteries from shore power whenever convenient to do so.

I have a battery charger for my car battery. Can I use this for my marine batteries, or do I need a specialised charger? If I can use my automobile battery charger, is it necessary to disconnent the battery before charging?

[BC Mike]

This is my opinion and may not be completely correct.
Yes and yes. Best to have an automatic charger of 10 amps max, why, because they are the cheapest that can do a reasonable job. Cost $60- in BC. I charge with all the cables connected.
Michael

[Weyalan]

My charger has a rated output of 2200 milliamps (2.2 amps). It stops charging when the battery is fully charged. Is this ok?

[Jon D]

In my opinion No

Car battery charges while inexpensive -- good are typically not smart charges in any sense. They are designed to get a charge into a single starting battery so you can start you car which is a surface loaded battery design. i.e. lot of juice short increment.

Your boat batteries are deep cycle. Little juice drawing down long time. When you deep discharge you need to charge them differently. That's why all current marine chargers are three stage - bulk, absorption, float. Unfortunately this is one of those penny wise pound foolish areas. You are much better off buying a decent charger to protect that bank cause odds are you will not be able to get it full charged or overcharge which can ruin batteries. Also if your plugged in the float cycle once batteries are charged really helps to reduce any sulfation.

[Strygaldwir]

The reason we have multi-step chargers is to minimize charge time on batteries with very large amperage capacities. It is not the most affective way of maintaining the life of a battery. The best way is to maintain a smaller current than the batteries acceptance rate over a significant time. This is, in the long run, is more beneficial to battery life.

Having said that applying charging amperage to a battery over an extended period is, as I understand it, the best charging method. There are a couple of issues, the first is that the charger you are using has enough IQ to stop when the battery is completely charged (Although most manufactures state that their batteries will take a 2% of capacity overcharge pretty much indefinately. ie a 200 amp hour battery can take 4 amp charge indefinately). The second is that if you're going to leave it hooked up, that the charger can supply sufficient current to meet the draw of any connected devices, the internal discharge rate of the battery, and have sufficient amperage available to actually charge the battery. If your car battery meets those requirements, you're going to be okay and won't damage, or decrease the life of the battery.

[Jentine]

Batteries are batteries and chargers are chargers. I would only be concerned with the overcharging of batteries left unattended but I would bet that you are smarter than a "smart charger".
I would no sooner leave a marine charger on all the time any more than an automotive charger. Use it but be careful.

[Alan Wheeler]

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.