Charging Batteries and Battery Chargers
Battery chargers are usually very simple things. The average manual charger is just a beefy transformer, a few large diodes and not much else. They often have less than wonderful internal connections and always benefit from a case removal, some soldering of the crimped connections and maybe some extra heavy wire. They usually have a circuit breaker somewhere and may have an alleged amp meter which imagines it can read current, more or less, approximately, somewhat related to reality. They produce pulsed DC with no filtering at about 15 volts. Some have a "fast charge" setting that really abuses the battery with even higher voltages. They are designed for very occasional use, expecting the battery to be routinely charged by a car's regulated charging circuit, not to be the only source of recharge for a battery.
Such simple chargers are good for pounding on batteries. They will easily overcharge batteries of the lead/acid type they are designed to work with. This causes electrolysis and gassing which damages the battery and makes an explosive gas (hydrogen).
There are some "automatic" chargers available at places like Sears for just a bit more than the equivalent manual ones. They are well worth the extra price when your primary use for the battery is portable or emergency power and a lot of recharging will be done off this charger. They are highly recommended over the manual versions.
The best battery charger is a power supply that can be current and voltage regulated. There are some super fancy automatic ones that incorporate these features. Based on the chemistry of a battery, there is a MAGIC voltage where it can be left connected and it will not overcharge, and its internal leakage will be compensated for, keeping the battery fully charged all the time. This is called trickle charged or "floated", but most so called trickle chargers are junk, not voltage regulated and really just slowly boil away the electrolyte with electrolysis, making certain it will be a "late" battery when you actually need it.
To properly charge a battery, you should apply a voltage that causes current to flow (being careful to get the plus and minus hooked up properly!) at about 1/10th the amp/hour rating of the battery to a maximum of about 1/4th the amp hour rating of the battery.
For instance, for a 45 amp/hour battery you should not charge much faster than 5 amps. For a 12 amp/hour motorcycle battery you should not charge faster than about 1.5 amps, etc.
When the voltage required to maintain this charge rate exceeds 14 volts, you should turn it down and regulate it at 13.8 volts. Just let the charge rate drop naturally while the voltage is held constant at the battery terminals.
Eventually the current into the battery will drop to practically nothing at 13.8 volts if it is lead/acid. Different chemistries will have different magic voltages. This is what is called "float" charging a battery. Maintaining it at a voltage which just balances the electrochemical potential of a fully charged series of cells, just below where they will start to perform electrolysis on the battery solution. If done correctly such a float can go on for a very long time and the battery will stay healthy, just compensating for the internal discharge rate of the battery.
http://www.chem.hawaii.edu/uham/bat.htmlI do not feel i need to comment any further on this, if you want to mess up your battery, go ahead.
