Segway lithium-ion battery repair with an increase in capacity by 30%

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Hello friends!

Today we are repairing the Segway battery. There are no brand markings on it, so it is difficult to name a specific manufacturer, it is only clear that it is Chinese, for a voltage of 36 V and a capacity of 4400 mAh.

This is how it looks from the reverse side. The connector for connecting to the controller is visible, and the charging connector is located at the end, and is closed with a rubber cap.

Unscrew the screws and open the cover. Having disconnected the balancing connector from the control board (BMS), we measure the voltage across it — on each block of cells.

In our case, 4 out of 10 blocks are discharged to zero, and on the rest the voltage is from 2 to 3 volts, which also does not mean their viability, therefore it is easier to replace all cells.

Judging by the specific smell and obvious external signs, one of the cells was depressurized and the electrolyte partially leaked out of it, destroying the balancing contact.

We solder the balancing and power wires, and then remove the insulators from the electrical cardboard. The photo shows how the electrolyte changed the color of several cells — from blue to pinkish.

We take out the battery and remove the remnants of the hot melt glue that held it. Thanks to its many ribs, the battery case is quite sturdy.

For the new battery, we will use high-current YLE cells with a capacity of 2900 mAh. We glue them by analogy with the old battery.

We will use spot welding for the connection. Unlike soldering, it gives a better and more reliable connection, and practically eliminates the depressurization of the cell.

If you do not have access to the welding machine, you can use the cells on which the contacts are already welded, and these contacts can be soldered together. For example, those available on Aliexpress.

After welding, we got the same blocks as the old battery. For the convenience of work, we sign balancing and connecting contacts.

We glue the end insulators — we managed to remove them from the old battery, while preserving the adhesive layer.

We put new blocks of cells in the body, in place of the old blocks.

We connect the blocks together, solder the balancing and power wires, and then check the voltages at the balancing connector.

Since all cell voltages are the same, we connect the BMS control board. We return the insulators from the electrical cardboard and close the case, and then check the battery in operation.

The declared capacity of the old battery (when it was in working order) was 4400 mAh, that is, it used 2200 mAh cells connected according to the 10S2P scheme. The new battery is assembled according to the same scheme, but from 2900 mAh cells, and its capacity was

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