New Project. Smart Aux Battery

Hi everyone! Fantastic forum.

We are in the beginning of a new project designing a new battery to offload the oem charger and many others features. i'll edit this message with updated information.

Summary:

This new device that replaces three oem parts on the oem parts catalogue.

- The botton plastic tray -PP MD20-. OEM Ref: 648946487R
- The battery terminal protector and locker. OEM Ref: 244204447R
- The 12V 14Ah Battery. OEM Ref: 24410309R

To one unique part:

- its a little thicker but fits perfectly on the battery "available room".
- Compatible with battery oem wiring terminals. -Five mm holes on terminals-
- No final measurements but its about half of the weight of oem battery and parts.
- From 14Ah to near 150Ah to let malfunction of the 12v main charger or feed extra accesories onboard.
- From AGM to LiFePO4.
- Charges directly from 230V plug in less than 3 hours so always when you charge your twizy always your aux battery is charged at max.
- The "smart" part of the name is about canbus. Its directly conected to canbus to send a collection of info objects that will be readable via ovms or any can bus tool about the included BMS.
- 100% compatible with OEM vehicle. With the 12V part of the oem charger working fine or not. It informs via canbus that the 12V its fine to avoy STOP light on the dash board and the three beeps.
-

.... more info coming. The advance of this post is about if anyone interested in testing or include more features during this milestone of finish the design process.

Thanks in advance for your support and thanks for this incredible forum.

Hello twizylover,
Welcome to the Twizy forum!
That sounds like an interesting project. Looking forward to further updates.

Welcome to Twizy forum.

twizylover schrieb: We are ...

It would be kind if you could introduce the team and yourself in a few sentences.

We are... a group of crazy and friend engineers and twizy lovers which thinks that twizy could have a second life with aftermarket parts improving original design. Sometihing like Andrii is doing in Poland but in Spain. Hopefully we can collaborate together in the near future. With our Smart Aux Battery, out future alternative of the sevcon, the Adrii BMS, Dashboard and the upcoming huawei charger... etc all the twizy owners and lovers has an option to continue using it.

Update. October 29, 2025;

Finally, We decided to use the maximum available space for future use to increase battery capacity or other purposes, with no new battery case payment.

You can see all space availble in the attached file SmartAuxBattery.Location.png. With the first case prototype i'll share final dimensions. In any case with this implementation all the poles will be waterproof in a sealed environment. If you analyse the img, you can see at the bottom end, a clearly rusted signs on the chassis by the Polypropilene tray -648946487R-. You can see the "rusted pattern" on the second attached img 648946487R.Tray.Bottom.png. The new battery case bottom will protect this chassis area.

Thanks in advance.

P.S.: Your comments are really welcome!! New feaures anything that you can think that will be usefull for you or anyone else!!

Nice Project. But WHY? The Twizy works well with a 12V 3AH battery if the battery is OK. I don't understand why you want to install a big and heavy 120AH battery when you have more than enough power available in the traction battery?

Where is my mistake by trying to understand the project?

I am worried there is a little "scope creep" here. You can and should not alter the twizy electric system architecture. The 12V battery is only used to get the main battery breaker closed on startup, and backup for hazard lights in case of "HV" system failure. BUS connection is a nice feature ideed.

I my opinion, main objectives should be (ordered)

- high robustness and reliability. Waterproof, shockproof, vibration tested, esd & lightning-proof, Wide Temp Range maybe -20°C to 65°C
- less weight than Lead Acid
- higher lifetime than Lead Acid
- attractive price compared with lead acid and off the shelf LiFePo blocks.

I currently use cheap off the shelf 6Ah LiFePO4 blocks without noticable issues. The only valid point of using bigger capacity cells would be to get the allowed charge current up to the specs of the charger. LiFePO may be a bad choice without heating pads, even newer cells dont like being charged below freezing temp. Weight saved on the 12V battery can be better used including a bigger traction battery. Extra Mains charging circuit will increase complexity and weight while hurting reliability.

Moin.

Switching from lead to Li-whatsoever Cell tech is not a bad idea at all, if the BMS can handle the crazy charging Levels of the original Twizy Charger. Imho they can rise up to near 15V at low temperatures. But as TC wrote, there is no need for a bigger Aux Batt. If the LI solution fits into the original Space _and_ provides more Ah, all will be good.

TwizyChrisy schrieb: Nice Project. But WHY? The Twizy works well with a 12V 3AH battery if the battery is OK. I don't understand why you want to install a big and heavy 120AH battery when you have more than enough power available in the traction battery?

Where is my mistake by trying to understand the project?

Thanks for your question TwizyChrisy, because the complete answer could be useful for others. Tonight i'm going to reply you in a complete way, but for now, a important note about weight, because was a very important point in our designs, origin of many discussions at that point.

In our recent data, all the batteries that we check, all of them was between 4000g and 4200g, Renault oem and Exide EK143 both 244103090R. In the picture attached you can see the official version of oem in 4045g.

In our solution -not finished the cell selection yet-, but for now we are currently testing eight LiFePO4 cells of about 22Ah each in a 4S2P configuration, that is about 44Ah (aprox x4 oem value) with less than 1000g more like that is a water bottle with you. In NCM or other chemistries we can improve energy density with the same weight, but we like a lot more lifepo4 batteries for 12V configurations.

How many AGM batteries you will going to buy in the next two decades? 4? one each five years?. With this solution you have battery forever -more than 4500 cycles on LiFePO4-.

Sorry for the little time, but many other advantages i'll answer you tonight.

Thanks in advance for your support.

Meine 12 Ah Lifepo-Batterie in Original-Twizybatterie-Größe (siehe Batteriealternative-Thread) hatte 40 € inkl. Versand gekostet, danach nur noch 30 €, jetzt ist sie wieder teurer.
Gewicht: 1,7kg. Die Blackbulls hatten bei mir leider nicht lange gehalten, weil das automatische Nachdaden nicht zuverlässig funktionierte.
Bisher funktioniert sie völlig problemlos, auch das automatische Nachladen funktioniert damit perfekt, aber ob sie auch den Winter übersteht, muss sich erst noch zeigen.

Pfälzer68 schrieb: Moin.

Switching from lead to Li-whatsoever Cell tech is not a bad idea at all, if the BMS can handle the crazy charging Levels of the original Twizy Charger. Imho they can rise up to near 15V at low temperatures. But as TC wrote, there is no need for a bigger Aux Batt. If the LI solution fits into the original Space _and_ provides more Ah, all will be good.

One clarification here, in the first design, the system only charges from 230V input. This battery charges when you plug your twizy -if needed, this means that only charges when its below 30%. Note here, the 30% of a 44ah battery is more than the 100% of oem battery so no risk at all to get a litle below 30% to wait for the next traction battery charge. This procedure keeps the health of the battery to extends his battery life instead charging in any moment when are on the go. And more important, if you have any issue with the onboard 12V charger section, or wth the 14.6V energy exchange feature of the charger, its not a problem, the twizy will works.

Thanks for your comments!!

FlipFlop schrieb: I am worried there is a little "scope creep" here. You can and should not alter the twizy electric system architecture. The 12V battery is only used to get the main battery breaker closed on startup, and backup for hazard lights in case of "HV" system failure. BUS connection is a nice feature ideed.

I my opinion, main objectives should be (ordered)

- high robustness and reliability. Waterproof, shockproof, vibration tested, esd & lightning-proof, Wide Temp Range maybe -20°C to 65°C
- less weight than Lead Acid
- higher lifetime than Lead Acid
- attractive price compared with lead acid and off the shelf LiFePo blocks.

I currently use cheap off the shelf 6Ah LiFePO4 blocks without noticable issues. The only valid point of using bigger capacity cells would be to get the allowed charge current up to the specs of the charger. LiFePO may be a bad choice without heating pads, even newer cells dont like being charged below freezing temp. Weight saved on the 12V battery can be better used including a bigger traction battery. Extra Mains charging circuit will increase complexity and weight while hurting reliability.

No worries, in dust, water and temp protection our target is IP69K.

In other hand, talking about shockproof and vibration we are testing a custom silentblocks at bottom inside the case to handle some Gs. We will try to pass the tests of MIL-STD-810 / IEC 60068.

Thanks for your comments Flipflop!

Welcome to the forum and good luck with the project.

This forum has a lot of knowledge and the guys above are really experienced and are great contributors to the Twizy community and really made a difference - and still they - typically German - sound all negative instead of being happy that there is another bunch of smart people around now trying to improve our little babies.

TwizyChrisy schrieb: Nice Project. But WHY? The Twizy works well with a 12V 3AH battery if the battery is OK. I don't understand why you want to install a big and heavy 120AH battery when you have more than enough power available in the traction battery?

Where is my mistake by trying to understand the project?

Complete answer, in a table for better understanding, sorry for the late:

Use case	Standard 12V 14Ah	||	New Smart Aux 44Ah	Description
1. Offload traction battery	NO	||	YES	None of the 12V systems will draw traction battery energy improving mileage.
2. Sizing for connect new accesories.	NO	||	YES	Connect freely audio systems, hvac system, ovms, displays, automatic doors, central lock, ambient lights, more powerful external lights, quick charge of your devices... without drawning traction battery energy.
3. Charges from 230V input	NO	||	YES	Charges directly from 230V main input and from onboard charger if needed. The oem battery only charges from main charger.
4. Works with fail in onboard charger 12V line	NO	||	YES	If your have your onboard charger with the 12V part broken -as many of us, and all of us in the future because its a known bug-, but Twizy will starts with no errors.
5. Vibration, Shockproof.	NO	||	YES	The oem service battery system has no vibration or shock protection at all. We will try to bypass MIL-STD-810 / IEC 60068 tests. This lets projects like offroad twizys or similar environments.
6. Water, dust, mud protection.	NO	||	YES	We will try bypass IP69K tests. The oem AGM battery has no protection. We have evidences of corrosion on terminals, chassis... etc.
7. Status information on CanBus.	NO	||	YES	The oem battery has no connection to canbus only voltage value is present. All the BMS information will be available on canbus like traction battery.
8. Weight.	4Kg	||	5kg	For the cost of the weight of one water bottle you have liters of features... haha.
9. Lets main charger replacement projects easily.	NO	||	YES	if you plan upgrade or change the main charger, you have a peace of mind about 12V part.
10. Minimum lifespan in cycles.	450	||	4500	AGM batteries often have a lifespan about 300-500 cycles. LiFePO4 cells selected about 4500 cycles.
11. Antithief system.	NO	||	YES	If you not are in place the twizy don't starts. We are developing a remote master soft-switch to avoid start if someone stole you the keys.
12. No need for a dedicated charger.	NO	||	YES	if for some reason, you need to charge the battery, you always can do it at home with the cable of any standard home appliance. No need to buy the typical 12V battery charger.
13. 2x USB-C PD3.0 Ports for dashboard.	NO	||	YES	Two usb-c PD3.0 ports connector to integrate on dashboard. Charging your devices directly from aux battery.
14. CanBus standard connection point.	NO	||	YES	In addition, we included one female Deucht Mini 4 pin connector, so you can get here canbus line and 12V with no touching oem cable harness.
15. Surprise feature #1.	NO	||	YES	Still studying possibilities.
16. Surprise feature #2.	NO	||	YES	Not enough info at the moment.
17. Price worth it.	YES	||	YES	The ratio relation between features, capacity and price its better for LiFePO4 vs AGM. and all the new mechanical features, but oem battery always will be the cheapest a simplest option.

I hope this helps to understand better the project, Any feature request?

Thanks in advance for your support.

P.S.:

... when you have more than enough power available in the traction battery

To be honest, you are the first person in the world that said that about Twizy...

Zyklenanzahl klingt natürlich gut! Die AGM sind ziemlich schnell am Ende.
Diebstahlsicherung ist ein Feature, wobei die originale Wegfahrsperre schon ein großes Hindernis ist.
Korrosionsschutz ist ein guter Ansatz!

Den Energiegehalt der 12V Batterie zu verwenden um den Traktionsakku zu schonen ist für mich wie
LED Leuchtmittel einzubauen um Reichweite zu gewinnen.
Bei einer nutzbaren Kapazität von sagen wir mal die große neue Batterie hätte 200 Wattstunden mehr als die Originale,
dann wären das irgendwas um die 1-2km......