SLI (Starting Lighting Ignition)
Conventional starting battery, flooded lead-acid. Not suitable for Start-Stop. Typical service life 3-5 years.
SLI (Starting Lighting Ignition) is the traditional category of automotive battery: optimised to deliver a high current pulse for 1-3 seconds (engine cranking) and then recharge from the alternator. It is flooded lead-acid with maintenance caps (some modern versions are "maintenance-free" but not sealed). It does not tolerate deep cycling (discharges above 30% rapidly degrade the plates). Today it is restricted to vehicles without Start-Stop systems (most cars built before 2012, basic city cars, simple commercial vehicles). Typical lifespan 3-5 years. Cheaper than AGM (£40-80 vs £90-200). If your car has Start-Stop, do NOT use SLI — the ECU detects it and disables the system, and the battery will die within months.