12v battery charging


(Peter) #1

According to the Renault Twizy vehicle user manual the 12v battery is charged as follows:

12 volt battery
The second battery on your vehicle is
a 12V battery: this supplies the energy
required to operate vehicle equipment
(lights, washer/wipers, etc).
The 12 V battery is charged either:
– when the traction battery is charged;
– when the ignition is on;
– when the ignition is off and periodically,
provided there is enough
power in the traction battery.

After not using my Twizy for 9 days, with the PowerBoxBT left turned on (traction battery fully charged), my 12v battery is completely flat and when the key is turned nothing happens.

Theoretically the 100mA load of the PowerBoxBT is more than sufficient to discharge the 14Ah 12v battery (0.1A x 24 x 9 = 21.6Ah).

I expected the 12v battery to keep itself topped up from the traction battery but this seems not to be the case.

I plugged the Twizy into the mains and initially nothing happened but after a few minutes it started to charge the traction battery, which was still showing 98%. I assume this started when the 12v battery had sufficient charge.

It seems my 12v battery charges when the traction battery is charged and when the ignition is on but not periodically when the ignition is off.

This isn’t a big problem as all I need to do is remember to turn off the PowerBoxBT.

I’m now wondering whether this is a fault or just normal? After reading many posts about the 12v battery I’m inclined to think the 12v battery doesn’t keep itself topped up when parked as the manual suggests.

(Peter) #2

Further to the above I have today done a bit of measuring with my multimeter.

As stated in the manual the 12v battery is charged when the traction battery is charging.

It also seems the 12v battery continues to charge when the traction battery is full (fans and screen off) but the mains is still plugged in.

With the PowerBoxBT turned off the standby current of my Twizy is ~12mA, which will theoretically drain the 12v 14Ah battery in ~48 days.

With the PowerBoxBT left on the standby current of my Twizy is ~205mA so the 12 battery will be flat in ~3 days.

The conclusion is I need to get into the habit of turning off the PowerBoxBT.

(Peter) #3

Further to the above I’ve since found this in my service manual.

From 15/08/2014, a system to maintain the charge of the auxiliary battery will be fitted to the vehicle.
Part numbers for the first generations of charger not taking the charge function of the 12 V battery into account during the vehicle sleep phases: 296054684R, 296055169R, 296052118R, 296051612R, 296058331R, 296050008R.
To prevent discharge of the auxiliary battery when the charging plug is not connected, a charging program for this battery has been implemented. Without any external visual sign, 35 minutes after switching off the + after ignition feed, the charger activates and charges the auxiliary battery if necessary. The charger uses the voltage of the traction battery to recharge the auxiliary battery. If the charge percentage of the traction battery is less than 15%, this recharge function is not authorised or is cancelled.

My Twizy was registered on 16/02/15 so may have been built prior to this modification.

I need to check the part number of my charger. I hope it’s not an early one as I specifically went for a later model for the upgraded charger but not too late for the PowerBox.

(Peter) #5

Due to a further 12v battery charging issue I’ve removed and dismantled my charger today to check for any water ingress.

All seems ok but it looks like my 2015 registered Twizy is actually fitted with a 2012 charger!

(Peter) #6

Further to the above I have since replaced my charger due to it failing to charge the 12v battery under all conditions other than driving fast!

To conclude, I have done some tests with my new charger fitted.

When the ‘ignition’ is on, my Twizy is charging or charging is complete but my Twizy is still plugged into the mains the 12v battery voltage is maintained at around 14.4v.

This is the interesting part. When my Twizy is parked the voltage measured at the 12v battery never falls below 13.2v, periodically jumping up to 14.5v for around 4 minutes. After my Twizy was parked for a couple of days, this was happening about every 40 minutes - see chart below.

This seems a bit excessive, especially as a relay is pulled in every 40 minutes!

Maybe this would be different if I fitted another new 12v battery, now my charging issues are resolved?

(osbrook) #7

I doubt it. The voltage on the 12v battery isn’t dropping very fast.

(Peter) #8

I think I’ll leave it for now and see how it goes.


(Peter) #9

I carried out a further test today, measuring the 12v battery standby current.

During the period the voltage is low there is ~12mA being drawn from the 12v battery.

During the 4 to 5 minutes the voltage is high, the current into the battery is as shown below (samples every 15 seconds).


I’ve done some further calculations and this is negligible compared to the 6.1kW traction battery at ~0.006kWh per day (providing my maths is correct).

I’ve put it all back together and now intend to do less testing and more driving!