I have 2 electric bikes:

• A small scooter-style bike of the Nicom Prince family (or Emmo Urban). This bike has a 14ah LiFePO4 48V pack
• An open-frame cruiser-style bike to which I added a kit. This bike has a 10ah 48V LiFePO4pack.

I am thinking of buying (or building) a 3rd "portable" LiFePO4 48V pack that I could carry around with me in my saddlebags on either bike to be used in case I run out of juice on the main pack. I would only take this with me if I knew I was setting out on a relatively long trip. (For anyone who is in my age group and remembers, this is similar to the early VW beetles - which had no gas gauge, but only a switch to a small emergency gas tank if the main one went dry).

Anyhow, I was thinking to keep it small and light, something like 5ah 48V would be adequate. Anyone seen such an animal? or would I need to build it (which I've never done before)?

Also any thoughts on whether this is a nutty idea or not are welcome...sort of!

Good luck with that!

It is an interesting idea though. I’ve seen people use small 5ah batteries for some lightweight short range 36v bikes. With 48 volts you are going to get, what, 5-7 mile range? It rather depends on your speed, your current draw, and your controller.

Personally, I just pedal if I run out of juice, but that may not work for you.

Here is what I recommend: Get someone like EM3ev to build you a custom Lithion-ion (18650 cell based) pack. LiFePo4 is going to be heavier and a little more expensive. But if it is for occasional use, the extra recharge cycles of the LiFePo4 isn’t that important. If you want LiFePo4, maybe ping could build you something.

The trick of course is C rate. I don’t know what your amp draw is, but a 5ah battery would need at least 4C to give 20 amps. You would be better off with 8C to keep from overstressing the batteries.

Then again, if you felt comfortable with LiPo, you could get a battery for about $80 to do what you are asking (plus charger and other doodads). 12s should be OK since you don't want to be going too fast (assuming of course your controller doesn't have a low voltage cutoff too low).

Here you go. Just get two of these and connect them + to - and you'll have 44.4v. It will give you what your looking for.

https://www.hobbyking.com/hobbyking/s...Search=5000mah 6s