Choosing a battery
Considerations when choosing an ebike battery.
The most commonly used batteries used on endless-sphere are:
- LiFePO4: Safe and "plug and play". But low C-rate, so obtaining required peak power can result in a heavy battery.
- Lithium Polymer (LiPo): Small, lightweight, cheap. But risk of fire or explosion if charged incorrectly, discharged incorrectly or punctured.
- Lead acid: Cheap, readily available and can have good lifespan if treated correctly. But heavy.
Other less commonly used batteries include:
- LiCo - laptop cells, such as 18650 cylindrical cells
- NiMH / NiCd - Used in small domestic batteries and Toyota Prius
- LiMnO4 - Not that common, nominal voltage 4V, maximum about 4.5V, low energy density when compared to LiCoO2
- LiNiO2 - high energy density, nominal voltage 3.5V, maximum about 4V, no lower than 3V on deep discharge
- LiCo1/3Ni1/3Mn1/3O2 - higher energy density than LiCoO2, 3.6V nominal, maximum about 4V, no lower than about 3V on deep discharge
- LiNiMnO2 - very high energy density, not yet commonly available, 4.2V nominal, maximum and minimum not known
A few questions to consider when choosing a battery:
- What range do you need?
- On what terrain?
- Carrying what load? (total weight, vehicle, cargo, you)
- At what speed?
- Continuous run at speed, or stop-and-go traffic?
- Can you recharge at destination(s)? (or along the way; would you have the time to do so?)
- What budget do you have?
That will tell you what kind of power requirements you will have. Then you can begin to pick out your drive system, if you don't have one already.
That will then help you figure out what kind of battery and what size you need, and then you can start looking for something that will fit within those limitations, and still work on your vehicle. If what you need is too large, then you might have to compromise on some of the specifications.
If you pick a battery based solely on weight and size, it may be completely insufficient to do the work you need it to.
For more on C-rates, see Rechargeable battery basics.
Many different battery locations are used: rear rack, within the frame, handlebar rack, seat post bag, pannier bags, top tube bag or in a backpack. Each location has advantages and disadvantages.
Adding weight to a bike can make the bike handle poorly. Especially if the weight is at the rear and up high. With lighter batteries (eg LiPo), the effect of battery placement is not as noticeable, so it is less important to mount the battery in the ideal location for handling (which is low and between the wheels).
I can't decide on a chemistry/technology!
Basically it depends on:
- your budget,
- your limitations in knowledge/abilities/willingness to learn,
- your system requirements for current/capacity/etc.,
- your available vehicle space to place them and weight limits,
- your patience with personally monitoring charge/discharge or buying the right kind of reliable monitoring system to do it for you, or getting something that is not *as* critical to do that for. (it matters with all of them, just a lot more with certain ones).
Balancing: Should you not buy packs that are already paralleled? Is it possible to simply extend the pack after some use?
Balancing is important for *all* chemistries, though when they are "new" many types may not need balancing--as they age they will, though, as some cells lose capacity before others, or get higher Ri, etc. Some require an external balancing setup, and some like NiMH and NiCd do it via the main charger leads in an internal chemical process (making a lot of heat).
You can always parallel more sub-packs or whole main packs together for more capacity, evne if it is just by their main leads, letting each main pack's BMS take care of balancing or LVC/HVC/etc. Doesn't matter what kind it is, other than NiCd or NiMH (those you don't really wanna do taht with).
*See - LiPo vs SLA