Replacement battery with a bit more range made from new cells for the smart ED3

As well implemented as original

Actually it sounds simple and logical. Nevertheless, it is an absolute herculean task that Vanja and his EVclinic have accomplished here. Thanks to the original BMS, every workshop can service the smart with this battery and even service the battery with the Mercedes diagnostic devices. In addition, such a clean solution does not cause any surprises at some point later. The other control units handle the battery like an original one and do not need to be adjusted in any way. It's no overstatement when I say that this solution is as good as original.

Take a closer look at the battery and cells

The smart ED3 originally had 93 cells connected in series and thus achieved a capacity of 17.6 kWh. Its voltage window is between 310 V and 390 V, just like a typical 400 V battery. The original cells are still the only cells that were mass-produced in Germany for an electric car and were quite advanced 10 years ago.

EVclinic is now using used cells from a Ford hybrid in its battery, as there are apparently more than enough of them. Their key data are quite close to those of the original cells. But because they are more modern, they can handle higher currents and are also lighter. This has the advantage that the smart becomes lighter. Thanks to the new cells, the battery weighs 50 kg less, only two thirds of its original weight.

For this reason alone, the new battery makes the smart a bit quicker. But it's not just the weight that helps here. Also that the cells have a lower internal resistance and are significantly more robust under load, so there is less voltage drop. Meaning that more power is given to the motor with the same current.

In general, the prismatic Samsung SDI cells on the hybrid still have the advantage that they are subjected to significantly greater stress in a hybrid than in the smart. So they should be even more durable than the original cells. In order not to weaken the hybrid modules (12s) structurally, they remain as they are. So a total of three cells remain unused. If a cell becomes too weak, you can reconfigure the battery, disconnect the weak cell and add the unused one.

The finished battery not only uses the original BMS, it also uses the original fuse, the original HV contactors and everything else. So that it still has all the safety measures that the original one had. Since Vanja has been dealing with the original batteries for years, he was even able to eliminate a few serial errors in the software. This prevents deep discharge. More about the original battery and how to repair it here: smart ED3 17.6kWh battery repair (feat. P18051C / bricked BMS)

Although the battery has practically the same capacity as the original, thanks to the lower internal resistance it still allows for a slightly better range because it is more efficient. The original cells have an internal resistance of 1.1 mOhm, the new ones 0.98 mOhm. This gives the battery a realistic range of 140 km, originally it was about 100 km.

This also means that less cooling is required: But since the cells can be positioned better on the cooling plate, they are cooled and heated even better than the original ones. Another point that makes the whole battery even more durable than the original. In addition, the battery is of course designed in such a way that it can be repaired using standard tools and expertise.

How much does it cost and will there be a battery with more capacity than the original in the future?

An exact price has not yet been determined, but Vanja writes that it will be between €6-8,000. This includes VAT, 3 working hours for the replacement and leaving the old battery with him. With your the old battery and its cells he will then cost-effectively revive vehicles with original batteries that only need a few cells replaced. And of course populate the gutted battery housing with new cells for the next customer.

Vanja has not yet written anything about a version with more capacity. When I asked, he told me that he planned to achieve 36 kWh. When and at what price it will be available is not yet clear. But you can certainly assume that this will come. Of course also in the original housing. Retrofitting CCS would also be technically possible. But this would probably be quite expensive, as something like this would only have a very small customer base.