Using a 48v LiFePO4 battery as a 36v battery

Hello

I have 48v 20Ah LiFePO4 batteries from a previous 48v 500w ebike that I want to use for a 36v 250w new ebike.

I am wondering if it is possible to tabing into a battery pack at the point where it would supply of 36v instead of 48v and thus leaving a fourth of the pack unused. The BMS would still shut off when the cells run low and balance the pack out when charging. Would this work?

Not really. The part you are not using will remain fully charged, so when you try to charge the battery the BMS will go into balance mode right away and thus take "days?" to charge the battery. See my option 3 below.

The 3 options I would choose from are:

1. Run the new bike on 48V. If the controller can't take it replace the controller with a 48V controller. The advice I got about a decade ago when I wanted to go from 36V to 48V was to just try it and if the controller blows just replace it, since I wanted to go to 48V. In my case the 36V controller handled 48V just fine.

2. Purchase a 36V battery.

3. Take the battery apart and rewire it for 36V with a new 36V BMS and a new 36V charger. You can remove the unused cells and save about 5 pounds and have 16 extra cells for repair or other use. Or you can add cells to each parallel group and create a 36V 25AH battery and still have a few cells left over.

In all 3 cases, except maybe the 1st one, you will have to spend some money.

How about more info on 36v 250watt bike.