Battery chargers
While several different types of chargers exist, a domestic setting tends to have two types. First, the old-fashioned trickle charger supplies a pre-set voltage, with a variable rate current (typically up to five amps) that falls gradually as the battery gases. While trickle chargers are less likely to replenish a severely discharged battery, they increase the risk of overcharging, especially with AGM batteries, a situation that is particularly problematic for sealed VRLA designs that cannot be topped up with distilled water.
Smart chargers, such as the CTEK model (right), assess battery condition more accurately and provide several charging stages, including voltage pulses to help break down short-term sulphation, and they will not overcharge. Furthermore, dependent on model, they can cater for the slightly higher voltages dictated by AGM batteries. More advanced types have extra functions, including boosts that help mix flooded electrolyte (eradicating acid stratification), to ensure a more even acid strength throughout the whole solution, and extra programmes for cold conditions.
Yuasa warns not to confuse assessing a battery’s state of charge – measured in volts – with its state of health – measured in amps (EN). A battery may be fully charged, but still might not be able to deliver sufficient power to start an engine because of the wear-and-tear that results in the shedding of the active lead materials from the plates. Crude methods of assessing state of health, by extracting a large current, such as using a drop tester, can not only be hazardous but can also damage the battery.
Modern professional battery testers measure the internal resistance and compare it against the battery’s CCA value. While such expensive equipment is beyond the reach of many DIY motorists, we compared several battery readings from Yuasa’s professional battery conductance tester against those from Ring’s RSC612 smart battery charger (which retails for less than £100) and found them to be within 3%. Note also that advanced DIY smart chargers can also assess the performance of conventional alternators.