Of course, you can! But it shouldn’t be done at all.
Portable jump starters are designed to build up a certain amount of power. If the rate at which that power is being created changes, then it would no longer be able to hold enough power to start your vehicle. Overcharging any product reduces its lifespan significantly. This is especially true when talking about electronics since an overload in voltage or current can cause damage due to the sensitive electrical components inside these devices. Portable jump starters have fail-safe features built-in so they will shut down if their charge reaches 100%. So even though there may not be any noticeable damage on the outside, overcharge protection boards could have been fried and will therefore need to be replaced.
May I ask where did you get this information? Is it true?
Well, this is definitely an interesting question. I’m not 100% sure where this claim originated from but the best guess would be car forums which made their way up to public forums and social media pages. And you should really look into that.
What happens if I leave my portable jump starter plugged in for too long?
Just about anything can be overcharged, and a jump starter is no exception. Jump starters that list specifications for the 12-volt power supply contain a warning: “do not apply AC power to this unit – it will become hot and possibly damaged.” Usually, this warning is also accompanied by specific instructions on how long you can leave the device plugged in. The user’s manual for the Schumacher XP2260 jump starter recommends unplugging the unit after eight hours of charging time even if the battery indicator still shows as much as half charge remaining. Portable jump-starter models come with either one or two rechargeable batteries, each of which should only be charged individually; both batteries cannot be attached and recharged at once because they share a single power supply and charging cord, and overcharging one battery can cause problems with the other.
The best way to avoid damaging a jump starter due to overcharge is never to leave it plugged in overnight or for longer than recommended by the manufacturer. If you need to be away from your vehicle for an extended period of time (like at work all day), then unplugging the unit after eight hours of charging should prevent any damage from occurring. It’s also possible that even if you remove the jump starter as soon as it hits full power, something could malfunction inside and cause damage anyway; however, this risk is still much lower than leaving a device plugged in overnight without supervision because parts wear out faster when they’re being used. Never charge a jump starter or anything that’s attached to one for longer than recommended.
You can actually damage your jump starter by overcharging it so please remember to unplug once the green LED lights up on your unit.