October 2019

BY Frank Massey T he vehicle battery has for many years ceased to simply be a chemical storage device. Instead, it has turned into a critical integrated component within the electronics network. It is also increasingly responsible for the total electromotive force in electric vehicles. I will comment on this development later. Despite this, it remains little understood or respected by many techs. I will begin with some interesting technical facts, provided by Yuasa, our battery partners here in the UK. Many independent battery manufacturers limit the critical internal components to reduce cost, as well as to maximise profit and range application. Typical configurations include smaller cell capacity and increasing the electrolyte strength to artificially meet CCA ratings. Reducing lead content reduces reliability, specification, and lifecycle. The electrolyte has a direct effect on performance and lifespan. Increasing electrolyte strength to artificially meet capacity specifications will increase internal corrosion. The end of life is directly affected by the number of start cycles over time, this is the defining feature of 2/3/4/5- year battery construction. The battery begins its decline immediately following manufacture. The initial formatting drives impurities off the plates, as a result the peak CCA performance should be achieved. The peak performance period (lifespan) depends on its warranty specification. The final phase is a rapid decline in output and eventual failure. The correct action is to replace the battery before the final decay period, it often appears to perform normally during this period. Hands up, who checks batteries at the point of delivery? If they are below 12.4v send them back. Six cells at 2.12v produce a voltage differential of 12.72 fully charged. At 0°C a battery has 66% available capacity. Excessive heat can also have a negative effect on battery performance and accelerate failure and end of life due to plate corrosion, an increased in self discharge, and increased electrolyte loading. A 10°C rise in temperature will increase the self-discharge rate from 0.1v to 0.2v per month.10°C equals a 60-month battery life. 25°C equals a 36-month battery life. Plate sulphation is normal during battery discharge. When both plates are coated with lead sulphate, or when the plate voltage falls below 12.4v, prompt recharge will displace the lead sulphate. The battery will normally recover and perform normally. However, if allowed to stand it will crystalize and harden. The death zone of a battery rendering it unrecoverable is SG at 1.04, cell voltage at 1.9v, total battery voltage at 11.3v. Recovery is marginal from a SG at 1.02, and a battery voltage at 12.3v. Acid stratification accelerates failure and can occur due to cold weather and short drive cycles. The separation of acid has the effect of increasing the open circuit voltage while reducing the CCA performance. Superficial testing may show a healthy fully charged battery. Conventional flooded batteries should be maintained within 5% of its fully charged state if premature cell failure is to be avoided. Meanwhile, AGM batteries can operate normally with a 50% cycle rate. 24v systems and vehicles using two batteries require that both the CCA and OCV be in balance. This is also a critical factor with electric vehicles using lithium batteries, as cell differential will lead to differential cell charge and overheating. Stop/Start vehicles will be fitted with either an enhanced flooded (EFB) or absorbent glass matt (AGM) batteries. Key differences with EFB & AGM are: Extended life over conventional flooded batteries Improved temperature resilience Improved charging and cycle times Additional internal plate components Leak resistant to 55°C AGM performance improvements, Four-times extended cycle times Sealed plates at 1bar preventing loss of active material Very low internal resistance High energy yield Electrolyte absorbed in the glass matt; 100% leak free Hopefully by now most repair shops have a conductance tool. It applies a small load, current at approximately 1-1.5 amps. The load is proportional to the correct battery specification, provided the correct battery specification has been entered. The internal resistance and state of charge is checked against an algorithm providing a linear comparison with a load discharge test. We can also use a scope with a hall effect current clamp. This will provide real time voltage drop and current draw across the whole cranking spectrum, a healthy battery at ambient temperature will return at least 100 amps more than the CCA rating during the initial starter ring gear 26 AFTERMARKET OCTOBER 2019 TECHNICAL www.aftermarketonline.net BATTERY BANTER Despite their universal use across most vehicles, many techs still don’t really understand batteries, but they are a missed opportunity Right: Battery voltage current cranking RPM