Wednesday, November 21, 2018

Will a USB power cable constantly attached to my motorcycle battery draw power enough to kill my battery?

This article first appeared on Trade Nepal

Now-a-days I see a lot of accessories, especially for Royal Enfield riders which let them charge their mobile cell while they are riding. Seems fun and practical, virtually never letting your cell battery run out of juice. But does adding those extra load kill of the precious motorcycle battery instead ?
Power cables by themselves don’t draw any power, however, a small 12V to USB converter will draw power and eventually discharge your battery. That is drain it, maybe not kill it. Kill is such a fickle word. I take “killing” a rechargeable battery to mean effectively ruining it so it won’t take or hold a charge anymore.

The USB socket is 5V. Your cable converts the 12V battery voltage to 5V and will consume power while it is connected. However, the amount of power is very small. You can measure it by testing the current drawn with an ordinary multi-meter connected in series on a 12V wire. When there are no USB devices plugged in the power drawn will probably be so small that it will not be a problem if the motorcycle is in daily use.

However, when a device (especially a GPS) is plugged in, the power consumption will increase. A cell phone probably will not run the motorcycle battery down too badly, but a GPS will. It is easy to forget to unplug a GPS and then the next morning the battery is so dead that it needs to be replaced.

If you discover that your lead-acid battery has run flat overnight, it is very important to get some charge into it IMMEDIATELY. Sulphating begins as soon as the battery is flat and in a matter of hours there is measurable damage. A lead-acid battery shouldn't be allowed to discharge below about 30% if you want it to last.

At least install an inline fuse in the 12V cable. When you store the motorcycle then remove the fuse or disconnect the battery.

It is probably worthwhile installing a 4-port USB charger. You are likely to need power for more than one USB device.