The strength of the BMW M4 Coupé is evident in every detail.
Now that the cold weather is with us our car batteries need all the help they can get for that first start of the day. It is as well to note that although the electrolyte will show a higher specific gravity at low temperatures, the battery capacity lowers with temperature because internal chemical reactions slow down.
What can we do to keep our batteries in a good state? Well, some things are very basic; number one is to keep them clean.
Any dirt or acid fumes that accumulate on the top of a battery must be cleaned off to avoid conducting paths between positive and negative lugs. Much the same goes for sediment in the bottom of the battery casing.
It depends largely on the age of the battery, but a self-discharge of 0.2 percent to one percent of the battery ampere-hour capacity per day is possible.
The rate may rise with an increase in temperature and specific gravity value.
The answer, of course, is to put the battery on charge regularly, or keep it on trickle-charge. For the latter you will need to know the discharge rate to apply an appropriate charging rate. I believe a periodic charge is the easiest method.
Batteries have several thin plates rather than one large single positive and one large negative plate.
This construction is necessary because capacity is proportional to the total surface area of the plates. It is important that the electrolyte level should not drop below the level of the active plates, hence the need for regular level checks on batteries where this is possible.
When, as is inevitable with age, sulphation builds up on the plates, it reduces surface area and capacity. Recharging will normally get rid of the fine crystals so formed.
But if the battery is left in a discharged state for a long time, coarse lead sulphate crystals form.
A long slow charge maybe able to restore them to fine crystal state, but quite often the battery is ruined.
Battery lugs come in three main types; there’s the cap and screw, the lightweight flat type which is often affected by fungus corrosion and the far better clamp lug.
Whichever type of lugs your battery has, acid corrosion may cause high resistance between the lug and battery post and reduce available voltage.
This will be most noticeable on cold starts.
If when the starter is operated there is a click from the solenoid accompanied by dimming of the dashboard lights, check first for poor contacts at the battery. Clean off the posts and clamps and try again. If no improvement, check for faults along the starter cable and do not ignore the earth to the vehicle body.
Batteries may be damaged when attempting to remove stiff lugs.
If no puller is handy, soak a cloth in hot water and hold it against the lug.
Many batteries have been damaged by over-zealous knocking when fitting or levering when removing the lugs.
The size of battery is determined by the starting requirement. In temperate climates the battery must be able to crank the engine at 90-100rpm at least.
When it comes to renewal, most of us simply buy the same type as originally fitted. But seek professional advice if in doubt. - Star Motoring