Deep Cycle Battery Charger - Lead-Acid AGM, Gel, Wet Battery Chargers
Lead acid battery chargers are intelligent, microcontroller based battery chargers, being able not only to charge wet/flooded, AGM, Gel, pure lead, calcium and other lead-acid deep cycle, dual purpose or starting batteries, but also able to recover deeply discharged batteries, recondition and desulfate their cells, and to maintain the batteries charged over longer period of time.
Picking a good lead acid battery charger should not be of an issue, especially since such device can save plenty of money in the long run.
Battery Chargers Features and Specifications
When choosing right battery charger, there are few things to consider:
- battery type and voltage: most lead-acid battery chargers are designed for charging 12 volts (6 cells) lead-acid batteries. Since AGM, Gel, and wet batteries feature slightly different voltages, some battery chargers allow the user to preset battery type, while other battery chargers either test the battery and try to determine battery type, or just go for an average value.
- overcharge protection: in order to prevent battery gassing, most battery chargers have maximum charging voltage in the 14.7-14.8 volts range.
- reverse polarity protection: in order to protect the charger, battery and in the end, user, battery chargers should have reverse polarity protection builtin - when the cables are connected to the wrong battery terminals, battery charger turns off charging.
- spark-proof: when connecting the battery, voltage difference can lead to short, but strong current pulses, causing sparks. Sparks can cause fire and other damage - good battery charger should be spark proof.
- thermal protection: to prevent any damage to the battery and charger, battery charger should stop charging process if ambient temperature rises above some critical level, usually between 104 - 122°F (40-50°C). Note that batteries with metal jacket can withstand up to 176°F (80°C), but those are exceptions. Also, if the internal temperature of the battery charger rises above certain level, unit must be able to shut itself off.
- thermal correction: in order to test and recharge the lead-acid batteries properly over wide range of temperatures, battery chargers must include ambient temperature when 'calculating' proper charging voltages during different charging stages. Otherwise, low temperatures can cause the batteries to be overcharged, and high charging temperatures can prevent the chargers to fully charge the batteries.
- maximum charging current: to prevent the battery damage and gassing, maximum current must be kept below maximum allowed charging current. If the charging current is to low, charging process can be unacceptably too long - note that some manufacturers specify 'minimum' charging current, especially for deeply discharged batteries.
- number of charging banks: the simplest smart battery chargers can charge only one battery. But, larger chargers can be used to charge several batteries at once, while monitoring each battery individually. Such battery chargers cost more, but less than multiple single-bank chargers of similar characteristics.
- wall mountable chargers: some battery chargers are designed for mounting on the wall, while others come with wall mount kits. Placing battery chargers on a permanent position has many benefits, especially when charging plenty batteries regularly.
- water protection: most smart battery chargers feature at least minimum water protection (some droplets on the casing will cause no harm), but some of them are designed to be water proof even when being fully submerged under water - usually down to 1 m, but there are models that tolerate 3 m, or even more...
- warranty period: good battery charger protects not only the battery or the user, but also itself from use and misuse. As such, warranty period of smart battery chargers vary from 1-year to 5+ years. Larger and more expensive models are designed to withstand rain, sun, wind, snow and other conditions and still function properly. Although such features tend come with a nice price tag ...
- battery charger price: small, single-bank, smart battery chargers cost few tens of dollars/euros. Large, multi-bank battery chargers can cost few hundred or even more dollars/euros. Sometimes it is good to have slightly 'over-dimensioned' battery charger, but such charger generally tends to be heavier and more expensive.
- charger weight: depending on the intended output power, smart battery chargers can weight less than a pound, or sometimes even more than 8-10 pounds. Of course, it is not the same if the battery charger is intended for charging small fish finder battery or several banks of large, industrial batteries.
- charging modes/stages: smart AGM, Gel-cell, wet-cell battery chargers charge the battery via several stages, ensuring battery protection and longer operating life. Period of simple battery chargers consisting of simple transformer and Graetz (diode) bridge is long over ...
There are other details that the user might look for, but these are IMHO really the most important ones.
To properly charge deeply discharged batteries, smart battery chargers use different charging stages, depending on the battery's Depth of Discharge (DoD).
Most common charging modes are:
Stage 1: Analysis - battery charger test itself and the battery and determines battery and charging conditions. If the temperature is too high, or reverse polarity are detected, battery charger must notify the user via LED light and sound.
Note: some cheaper 'smart' battery chargers cannot sense 'too low battery voltage' and refuse to charge such battery (no connection condition). Good battery charger will detect even such battery and will try to bring it to life.
Stage 2: Desulfation - charger enters this stage if it detects battery sulfation or severe discharge and starts desulfating the battery through short pulses. Once the battery is rejuvenated and brought back to life, charger moves to next stage - Soft Start (if present) or Bulk Charge.
Stage 2: Soft Start - at this stage, battery charger starts gently to introduce the power to the battery, preparing it for the actual charge - Bulk Charge stage - when the most of the energy is transferred to the battery.
Stage 3: Bulk Charge - battery is charged using charger's highest rated current, until it reaches certain charge, usually around 80-90% of nominal capacity.
Stage 4: Absorption - the output voltage is limited to certain level (usually around 14.7 volts, depending on the temperature) while current slowly declines as the battery is charged to its full capacity.
Stage 5: Battery Test - after the battery is fully charged, charger can turn off the charging process and monitor for certain period of time (for example, one or more minutes) output voltage of charged battery. If the battery voltage drops below certain level (for example, 13.2 volts), battery cells are not performing equally and they must be conditioned.
Stage 6: Conditioning - battery is being charged with low current for certain amount of time (for example, 4-6 hours), giving enough charge and time for battery cells to equalize themselves.
Stage 7: Maintenance - in this stage, battery charger monitors the battery condition and charge the battery when required or after certain amount of time (for example, once a month).
These charging modes/stages are general charging modes and not all smart battery chargers features all of them, while some battery chargers even feature additional modes.
The Best Deep Cycle Battery Charger
Well, there is no such thing as 'the best' deep cycle battery charger - battery charger requirements are highly individual, and what is good for one person, doesn't have to be good for somebody else.
For short: when trying to buy a good battery charger, try to write down features and characteristics that your new smart battery charger must have and buy the battery charger that fits your needs perfectly - while such unit may not be the best battery charger for somebody else, it is the best battery charger for You. And that is all that matters.
Note: Batteries and battery chargers are not toys. Whatever You do, stay safe. If unsure, ask for professional help!