uh, no. I'll scare you off. Its a potential fire hazard (and you really, really don't want a Li-Ion fire - ever seen a tesla that burned??? (or the house it was in?)).
when you connect the two batteries, they will immediately try to equalize - with one battery charging the weaker battery - this will likely charge the battery too fast and can potentially cause serious problems.
It can be done (if you are an EE or equivalent), but you need to make sure you don't have a sudden unintended current flow. I'd say, if you have two identical batteries (including age) that are hot off the charger, its probably a low risk - but start changing anything and the risk goes very high.
At $15 a charger, I have two chargers - clearly charging two separately is going to take half the time then charging both off of one charger.
Me, I just carry two batteries, and switch from one to the other half way through the ride.
Ebike.ca did develop a cool little reserve tank battery that was designed to be used in series and you could plug and play as you liked. That would make a nice little reserve tank, but they were not cheap. Their primary goal was to make a battery small enough that you could ship it without incurring the Li-Ion shipping tax.
What specifically is your goal? Doubling your ride time? having a small reserve tank?
Originally Posted by
hydrocarbon
Trying to add an extra battery can cause a lot of problems if it isn't done right. I normally just carry an second battery when I need extra range and swap out when the first one dies. Less weight for trips where you don't need two, and fewer failure points under all circumstances.
One of my bikes does have the factory-fitted dual battery setup, but it isn't a big deal compared to just keeping it simple and swapping out two batteries with a standard single mount.
Yeah, what he said!