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.