Date: 15/6/2020
Batteries are more expensive than you think. Also how you wire them up is apparently important!!!
According to 300mpg.org volts \~\= speed. The advantage of converting a scooter and not a big bike, is that no one is expecting very much speed, so you can get away with a lower-voltage system - saving you cash.
Even once you have decided your voltage requirements there are a whole load of other things to think about:
1 Lead Acid or Li Ion?
Lead acid has the advantage of being cheaper, but the major disadvantages of being bigger, heavier and holds less power - oh and also if you drop the bike you’ll end up with acid all over your shoes. Li Ion is more expensive, but can hold more charge per cm^2, and will not cause your feet to melt when you drop the bike.
2 BMS
No one really talks about BMS’s, because it reveals a secret about batteries that battery companies have been trying to contain for years. Big batteries are actually just loads of small batteries put together! As far as I can tell, without letting the battery-illuminati know that I am on their case, most big batteries are just clumps of 18650 batteries wired in series and parallel to provide the current voltage and amp hour output (side note: amp hour, or Ah, is how much charge a battery can provide for how long. i.e an 80Ah battery can give 80A for one our, or 1A or 80 hours; or any combination therein). A BMS is a little circuit board that ensures that each of the little 18650 cells is equally charged, and that the power is not being drained from one faster than any other. A must-have for any battery of cells then… However, it is not clear that any battery pack online is equipped with a BMS - some of them say "BMS inside” or words to that effect, but that only makes it more suspicious when they don’t have that on the label….
3 Building batteries
Now that I have been inducted into the battery sanctum, it turns out that you can build your own battery packs to suit whatever specs you need to do that. This essentially involves spot welding conductive metal between the cells to join them in series/parallel. I think this is a really cool idea, but the idea of working with such big voltages scares me, so I think safer to rely on a trained professional to build my batteries for me. It does, however, mean that I can specify any size / shape battery that I wish - rather than relying on big clunky square ones.