How to make your battery last longer
QI’ve just replaced a battery that died after a relatively short period of service. Do you have any advice on using a ‘smart charger’ and generally getting the most life out of a battery? Simon Needham, Barkestone
AWe’ll start with ‘smart chargers’. These devices can charge a battery, then top it up indefinitely with a trickle charge. They do this by continually measuring the voltage at the battery terminals and administering the required current accordingly.
Cheap models tend to have a low maximum charging current, but this is not detrimental unless a rapid charge is required. Anything between four and ten amps will be adequate for most classic cars. It’s only a maximum, anyway – they’ll all drop to a few amps after an hour-or-two.
Better models also have a ‘desulphation’ function, which claims to reverse some of the natural symptoms of battery ageing by attempting to shock hard deposits off the battery’s plates with high-frequency pulses. This is not a panacea by any means – crusty plates is just one of several debilitating battery illnesses.
The biggest advantage of a smart charger is that it can be connected and safely forgotten about. It’ll adjust its own charging rate and switch itself off if the battery malfunctions.
However, these devices aren’t perfect. As a battery ages, it performs differently and the voltage at the terminals will start to differ from what the charger expects. The charger tries to respond to what a perfect battery would do – but it’s not dealing with a perfect battery. Thus, batteries are often declared fully charged and put into trickle-charge mode long before full charge is actually achieved. This is useless when you come to use it, and it’ll also shorten the battery’s life.
A good way to kill a battery prematurely is to keep it fullycharged and not use it. This is why stored cars with trickle-charged batteries can still fail to start on demand. It’s also worth noting that a smart charger will sometimes refuse to charge a completely flat battery.
In addition to a smart charger, therefore, you should kit yourself out with a simple oldfashioned charger. An unspectacular model will be perfectly adequate. It’ll cope with completely flat batteries with ease. Also, its broad-brush approach to charging – it outputs an unregulated 15 to 16V – is perfect for giving older batteries a slight overcharge to bring them back up to speed. It’s usually sufficient to charge a battery overnight, though one that’s totally flat may take up to three days.
Extended charging periods call for very careful monitoring. It’s a good idea to let it rest periodically. The battery’s fully charged when the specific gravity of the acid in the cells doesn’t rise any further over a period of three hours (use a hydrometer). At this point, it should be gassing enthusiastically (but
not violently) and it should be no more than comfortably warm.
The best conditioning you can give a stored battery is to leave the car’s headlamps on to discharge it, then charge it fully with an old-style charger. Do this every three months regardless of whether it’s left on a trickle charge.
If the battery has removable cell caps, check the acid level from time-to-time. There’s usually a dipper or a ledge moulded into the battery casing below the cap. It should be filled to this point. Top up with distilled water and give it a brief charge or a bit of use to mix the liquids. Never top up a totally flat battery before charging it: the acid level rises considerably and it’ll overflow.