How to replace a gate motor battery safely

A new battery won't help if the charger is the fault, and a surprising number of "dead" batteries are really chargers with no supply. Before buying one, check that the motor's own power is on and that it has had a full night to charge; our guide to a battery that won't charge goes through that. If the low-battery signal is still on after that, and the motor dies early in a power cut, the battery is the likely culprit.

Most domestic sliding gate motors take a sealed 12 V lead-acid battery of about 7 Ah; heavier motors take two, wired to make 24 V. The voltage must match, and the battery must fit the space in the housing. The surest way to get the right one is to read the label on the old battery, or send us a photo of it. Our battery page lists the standard battery for each common motor.

Every maker starts the same way. Centurion's maintenance instructions say to isolate the mains supply and disconnect the battery before working on the system, and ET says the household mains must be disconnected before the battery is removed. In practice that means switching off the motor's isolator or unplugging its supply, so nothing inside the housing is live from the mains.

If you can't find the isolator, or the battery can only be reached past exposed mains wiring, stop here. Mains work is a job for a registered electrician, and changing the battery is a short job for us.

How the battery is reached depends on the motor. On Centurion's D3 SMART and D5-Evo SMART, for example, the control card hinges forward and the base tray swings up to expose the battery on the lower tray. Then:

1. Note how the old battery sits, and which lead goes to which terminal, before you disconnect anything. A photo on your phone is the easiest record.
2. Disconnect and lift out the old battery, taking care that nothing metal bridges its two terminals.
3. Fit the new one the same way round. Centurion's SMART manual has the terminals facing the charger, and its D5-Evo manual stresses getting the polarity right: positive to positive, negative to negative.
4. Close everything up properly. On the SMART motors, the control card and tray must click back into place; Centurion warns that if they don't, the motor will behave erratically.
5. Restore the mains, then run the gate a few times to check it opens and closes normally.

Centurion's maintenance list asks for the battery terminals to be checked for corrosion every time, cleaned, and given a coat of copper-based grease. White or green crust on a terminal makes a poor connection and can make a good battery look like a bad one.

The motor itself is the first test instrument. Many motors report battery and charger readings on their own display:

• Centurion D5-Evo and D10: the battery charger diagnostic screen shows the charger voltage, which should read 13.8 V on a D5-Evo and 27.6 V on a D10, and each charger has a red light showing it has mains.
• ET Drive 500 and 600: the diagnostics screen shows the battery voltage and what the charger is doing.
• Any motor: a low-battery signal on the status light, and a motor that shuts down early. Centurion's D5-Evo stops at 10.5 V, and the D10 at 21 V, to protect the battery.

A voltage reading alone can flatter a worn battery, because it may show a healthy figure at rest and collapse as soon as the motor draws current. That's why we load-test a battery in place, with the charger, before recommending a new one. It's also why a battery that "tested fine" at home can still fail at the gate.

A lead-acid battery doesn't go in the household bin. ET's manual asks for a spent battery to be handed in at a battery merchant for safe disposal, and many battery shops take old ones back. When we replace a battery, we take the old one away.

Call us when the battery can only be reached past mains wiring, when the motor takes two batteries in series and you're unsure how they connect, when a new battery doesn't cure the fault, or when the charger needs checking. Centurion is clear that its charger fuse is only checked with the mains isolated, and by someone qualified, and that you shouldn't try to repair the unit yourself.

When we do it, we test the battery and charger first, fit a battery of the right voltage and size, clean the terminals, and test the gate before we leave. All our spare parts are genuine, and every repair comes with our six-month guarantee on our repairs. Same-day repairs are offered when the day allows. No call-out fee when we do the work. If no work is done, a R650 call-out fee applies.