Its not a good idea to charge a battery while its connected to your bike, I'd suggest you disconnect the earth lead.
The reason is, that most motorcycles use a "Shunt" type of voltage regulator. These regulators are the modern equivalent of the zener diode used on older bikes, and indeed usually use a zener diode as part of their design.
A shunt regulator is a heat-sink which diverts excess energy from the charging system from the battery to to heat.
For reasons known only to the designers, they are often wired so they are connected across the battery, even when the key is is off.
If you attempt to charge a battery that has a shunt regulator across it, your charger will be working against the regulator.
Your charger DOES NOT produce DC. Its an AC device, with a rectifier. A recifier gives you a varying current, but with a peak voltage much higher than its rated output. This varying current flow is all travelling in the same direction, so it suitable for charging a battery.
That little 4-amp 13.8 volt rated charger you got from repco will actually have a peak output voltage of almost 19-20 volts.
50 times a second, your bikes regulator will attack that peak voltage, trying to turn it to heat.
If the charger is small enough, the regulator will win.
Thats how your "battery tenda" etc work - they are designed to operate at a voltage that is high enough to charge the battery but not high enough to give the regulator any work. As long as they don't g over voltage you are fine.
If the charger is too big, or it does go overvoltage due to a fault, the regulator will loose.
Then the full charger voltage of up to 20 volts will be applied to your battery, and anything else in circuit at the time.
Bottom line ?
Take 20 seconds to take the earth lead off before charging your battery.
David must play fair with the other kids, even the idiots.
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