Does a motorcycle battery charge while idling? It depends fully on the motorcycle manufacturer, model, and model year.
A typical classic BSA, Triumph, or Norton would not charge when idle because they use a permanent magnet generator. So, the idle speeds can’t produce enough voltage to power the motorcycle battery. Most other motorbikes, including classic Harleys with similar PM magneto generator, would not charge the battery when idling.
On modern motorcycles, however, the battery may be charged when idling, except the air filter is blocked or the idle speed is abnormally lower than the manufacturer’s specification.
Can I charge the battery by leaving the bike idling?
Yes, you can charge the motorcycle battery by leaving the bike idling. However, it is not largely effective and won’t give the battery a reliable or full charge. Typically, most alternators merely push 1 amp into the motorcycle battery, which is insufficient to power the battery. But your motorcycle battery will charge while riding since the engine can rev over 10 amps (does not apply to slower riding).
Nevertheless, you can increase the idling speed for battery boost by throttling the motorcycle at 4000rpm for 10 minutes. The neighbors may not like the noise, so it is better to use a smart charger.
Does a Motorcycle Battery Charge While Idling?
A motorcycle battery will charge while idling, but it depends on the idle speed, the number of revs, and motorcycle accessories turned on. A motorcycle alternator is an engine-powered generator that charges the battery, but it must generate at least 13V to 14V. So, the alternator rotational speed should fall between 2,000-3000 rpm to power the battery.
However, the typical idling speed of a single-cylinder bike is about 1000-1200 rpm, while a multicylinder would rotate at about 1200-1300 rpm. Therefore, your motorcycle can’t generate enough voltage to charge the battery to a decent level, except you rev or ride it.
In essence, charging a motorcycle battery while idling can empty your gas tank quickly with almost no juice in the battery. How the motorbike manufacturer designs the charging system also determines whether idling charges or maintains battery juice. But in most motorcycles, idling will supply enough current to keep the battery juice on the plus or positive side.
Some modern motorcycles use automotive-type alternators so that your battery can charge while idling but at a reduced current output. Meanwhile, the higher the idle speed, the more power the alternator generates for charging. You’d also want to disable the lights and accessories to shift available energy to the alternator.
How Long Does a Motorcycle Battery Charge While Idling?
Honestly, how long it takes to charge a motorcycle battery while idling depends on many factors, including the battery condition, idling speed, and motorcycle alternator design.
There is no specific time regarding how long a motorcycle battery takes to charge in idle. But understand that the battery receives low current while idling and would not charge as fast as when riding the motorcycle. Typically, you’d have to ride a motorcycle about 2-4 hours for a full charge, so idling should take double the time. Also, about 15-20 minutes of idling can charge the bike battery to a not-so-reliable extent.
How to Know if Idling Can Charge Your Motorcycle Battery
To know if idling can charge your motorcycle battery, inspect the voltage across the battery using a multi-tester while idling. If the voltage is lower than 12.6 V, your motorcycle battery may not be charging. But at around 13.2 V or more, the battery is charging.
The typical max voltage is between 3000-5000 rpm, which would often not increase; perhaps it falls slightly. It is a good sign when the voltage increases gradually while on a stable idle. However, if it displays a V that rises faster, the battery has a problem and would need replacement.
Some motorcycles can charge while idling with lights on, depending on how the voltage regulation functions. If the manufacturer does not mention that your bike can charge at idle, make sure to disable the GPS, unplug your mobile phone, and turn off the lights for the stator to function robustly.
In essence, idling mostly gains charge at operational rpm and power accessories but does not entirely charge the better battery. If your battery is dead and won’t start, you can push start your bike.
You can always get a battery tender to avoid worrying about idle-charging the motorcycle battery.