Frank Massey of ADS Automotive boosts his workshop’s battery service.
The battery is the oldest electrical component fitted to a vehicle and due to a varying degree of complacency, I believe our industry has fallen behind in understanding its rapid recent development and has missed opportunities in maintenance, diagnosis and repair.
I can, with a degree of shame, admit to not testing batteries as thoroughly or often as we should have over recent years but we have rectified this over the past several months by taking part in the Yuasa battery testing programme. The programme has helped not just in updating our knowledge of battery technology, but has highlighted the need and opportunity in offering our customers a professional health and charge status report.
Our experience has shown that around 60% of batteries in vehicles coming through our doors are under
voltage and sufficiently down on capacity to warrant replacing. Before you assume this is a simple sales drive,
please consider how important the battery has become, its responsibility and effects on the reliability of
complex network systems.
Several vehicles, especially common rail diesels, have had the incorrect capacity battery fitted as customers often choose cost over application. This results in slow rotation speeds and delayed start problems. Stop-Start vehicles must have either EFB or AGM batteries if serious damage is to be averted. Also, do batteries fail
more in winter? Not necessarily, hot temperatures cause an increase in self-discharge!
The theoretical storage life of a battery is three months, with careful handling this can be extended to
six months. The minimum voltage should not drop below 12.6 volts – do you check new battery deliveries for
health and charge status? So, what’s the problem? If it’s a bit low recharge it, right? Note that each percentage
drop below 12.6V will reduce the cell capacity and its service life.
New batteries will not reach the full capacity until it has been formatted, this process forces impurities off the
cell surface. A battery voltage of 11.3V = SG1.038 or less is unrecoverable, scrap it. Battery capacity is a simple
matter of cell area, the more the better.
The traction battery is designed to provide a high current over a short period, to convert chemical energy stored in the electrolyte cocktail the cells are much thinner than leisure batteries. The traction battery should be maintained with a voltage above 12.6V = SG 12.55. The recovery range is 12.72V-12.36V.
THE RELATIONSHIP BETWEEN PERFORMANCE AND PRICE
What is a budget battery? Well I guess it’s much like all budget components, you get less. You may have noticed
a budget battery with the same performance rating as a premium brand. A common way of achieving this is to increase the acid strength. It may work in the short term; however, acid corrosion will greatly reduce its life span.
Acid stratification is a problem often brought about in winter when the battery charge falls below 80%. Short journeys and incomplete charge cycles, where insufficient heat is generated to reduce the internal resistance, are to blame. Hot temperature failure is interesting. Above 60°C you get accelerated plate degradation. Every 10 degree rise in temperature doubles the self-discharge rate of 0.1V to 0.2V per month.
How to test a battery depends on your technical assets. A minimum of a conductance tester is required; this performs both health and charge status by applying a small proportional current through the plates. PicoScope diagnostics has a test programme that analyses voltage drop against current consumption. Having entered the appropriate battery data and temperature, an algorithm calculates internal resistance.
Another practical test with the Pico is to conduct a similar test using the 600 amps clamp as well as monitoring
voltage drop during an extended crank non-start test. The essential observation here is to assess voltage drop against current rise times during the lock draw period, then observe the recovery period once rotation has been achieved. Next, calculate the rotation speed and average current draw based on the following formula.
Ampere hour rating x 3.5 = cranking amps.