Laying Up for Winter: How to Keep a Lotus Battery Alive Until Spring

The alpine passes are closing and the roads are about to be salted. A lot of Lotuses will spend the next few months in a garage, and the part most likely to suffer is the battery.

Why a parked car goes flat

Every battery loses charge slowly on its own, even when nothing is connected. On top of that, a modern car is never fully switched off. An alarm, an immobiliser, a tracker or the memory in the stereo and engine management all draw a small current around the clock. In a car that is driven every week, the alternator puts that back. In a car that sits for a whole winter, nothing does.

The light weight that makes an Elise or an Exige so good on a mountain road works against it here. These cars carry a small battery, so there is less charge in reserve before it runs down.

Why flat is worse than inconvenient

A lead-acid battery that is left partly discharged starts to sulphate. Battery University describes sulphation as a layer that builds up on the negative plate and blocks the flow of current. Caught early, a proper charge can recover some of the lost capacity. Left for months, the damage is permanent, and the battery will never hold a full charge again.

A discharged battery also freezes more easily than a charged one, which matters in an unheated garage. As a rough guide, Battery University suggests recharging a 12 volt lead-acid battery before it falls to about 70 per cent charge, which is around 12.4 volts at rest. Check your battery maker’s figures, as they vary.

What to do

• Charge it fully before the car goes away. A last long drive helps, but a charger is more reliable.
• Use a smart charger or maintainer. These charge the battery, then switch to a low maintenance mode and top it up only when it needs it. That is very different from an old trickle charger, which can overcharge a battery left on for weeks.
• If you cannot plug in, disconnect. Taking off the negative lead stops the drain from the car’s electronics. You may lose radio codes or settings, and the battery still needs a check and a charge every month or so.
• Check the battery type. Some cars, including the Emira 420 Sport with the Lightweight Handling Pack, use a lithium battery. These need a charger with a lithium setting. Do not use a lead-acid charger on one.

In spring

Before the first drive, check the battery has held its charge, look at the terminals for corrosion and make sure the clamp is tight. If the car struggles to start after a winter on a maintainer, the battery was probably on its way out anyway, and the spring is a better time to find out than at the top of a pass.

For the other checks before the first trip of the year, see the road trip preparation guide.

Source: Battery University, BU-702: How to Store Batteries.