Maybe you left the key on, maybe you wired that accessory up wrong...
We’ve all been there: we come back to our motorcycles and notice that we left the key in the “park” position, or, heck, just left the key on. Now the battery is dead. What to do?
Well, unless you’re deep in the woods with no outside electrical power and no other vehicles around, you have some options other than pushing it or attempting a bump-start (or removing the battery, hoofing it out of the woods, hitching a ride, recharging it somewhere, and then hitching another ride back to the bike).
If your first inclination is to bump-start the bike, know that's kind of a crap shoot. Some bikes bump-start really easily. All bikes are easier to bump-start in second (or third, depending on your gearing) instead of first gear. If your bike is fuel injected and your battery is really really dead, it may be impossible to bump start (no power for fuel pump means no gas, no go). If you're a pro at bump-starting your bike, that might be your best bet. If not, read on.
But first, a little bit about batteries!
The most traditional (oldest technology) batteries are simple lead-acid. They’re spillable, and they need maintenance. Remember that very old bike you had, whose charging system cooked batteries dry, and then you had to get in there and take the little yellow caps off the cells and pour in distilled water up to the “full” marks… Are you having nightmarish flashbacks yet?
These lead-acid batteries were prone to sulfation and needed regular charging or would go flat all on their own. They do not deal well with going totally dead, and if you’ve “deep cycled” your old non-maintenance-free battery more than twice, you should probably replace it.
AGM batteries are zero maintenance because their guts, while still technically traditional lead-acid, are an Absorbed Glass Mat: the innards are a fine fiberglass mesh which holds onto the electrolyte. These batteries are not spillable, and are maintenance-free.
Gel batteries are what they sound like: their electrolyte is mixed with silica to form a gel. They can be mounted in any orientation on your motorcycle. Both AGM and gel are less prone to sulfation, and can hold a charge without needing maintenance for quite a lot longer than the old lead-acid ones. They also both deal with a “deep cycle” or three much better, but again, if you regularly completely murder your battery, know you’re significantly shortening its life. An AGM will die with some warning, a gel battery tends to die suddenly.
Lithium Ion batteries are the newest tech. They’re lightweight, non-spillable, zero maintenance batteries with a Lithium Iron Phosphate cathode, a graphite anode, and Lithium ions in the electrolyte. These batteries are very prone to damage due to overcharging and are sensitive to temperature. They don’t work great in the cold and should never be stored in excessive heat. If you have put a Lithium Ion battery in your motorcycle and consequently run it flat, follow that battery’s manufacturer instructions for recharging. Overcharging these batteries can be very dangerous.
If you have a traditional lead-acid, an AGM, or a gel battery, you can safely recharge it with fairly traditional methods. Even with these old tech batteries, though: never attach jumper cables to your bike’s battery from a running car or truck! Your motorcycle’s electrical system can be irreparably damaged from the electricity a car or truck alternator can put out. You can, however, hook your motorcycle battery to a car battery, as long as that car is not running. Leave it hooked up for a few minutes, then try your bike.
You can also plug your bike’s battery into a battery charger or tender. Be warned, however, that some “smart” chargers will not even make an attempt if your battery is too flat. These chargers need some electrical feedback before they’ll begin their work, and will not revive a really dead battery.
Your best bet is a portable jump starter pack for 12V batteries, like this one here. They’re great for long trips and local brain farts alike. They will jump your bike and recharge your cell phone, and you can rescue your riding buddy whose battery has given up the ghost over lunch.
Friends, where was the worst place your battery has died on you? Did you accomplish a heroic MacGuyver-style motorcycle rescue?
Source: Battery University