Replacing the 12v auxillary battery on a Mitsubishi i-Miev, Peugeot iOn or Citroen C-Zero

This guide was written based on a UK spec 2011 Mitsubishi i-MiEV, which is of course the same vehicle as the Peugeot iOn and Citroen C-Zero.

All sizes are +/- 2 mm.

Before you start

Before you disconnect the 12v auxiliary battery make sure:

• The ignition is turned off

• You have waited at least 1 minute after turning off the ignition

• You have the radio security code

Replacing the 12v auxiliary battery

The 12v auxiliary battery in a Mitsubishi i-MiEV is very easy to replace. Access is easy and its held in with just one 10mm nut. All that is needed to remove the battery is a 10mm ratchet spanner for both the holding bracket and battery terminals.

However, sourcing the replacement battery is more tricky (in the UK). You can of course go to a Mitsubishi dealer, but I've heard they are £100. I've not checked this myself.

The original Japanese battery is a 34B19L(S). The battery does not have a label to indemnify the specs, but I believe it is a 27Ah battery. However, this isn't so important in an EV as the battery isn't turning over an engine. Its more the physical dimensions that make it tricky to source a replacement. The terminals are the UK standard size, rather than the narrow Japanese terminal posts. I would assume this is the (S) on the battery code.

The OEM battery size is approx: length 180 mm, width 124 mm, height 201 mm. The battery sits in a tray, which if kept, will limit the footprint of the battery to a maximum of 184 mm length x 133 mm width. The height is more crucial as the mounting bracket will only allow a battery of a maximum height of 204 mm (to top of battery, not the terminals).

When buying a replacement battery, most quote the total height to the top of the terminals, not to the top of the plastic case. So you have to deduct the terminal height, which is normally around 18 mm. You need to source a battery of less than 204 mm in height (or possibly 222 mm to the top of the terminals).

The size of battery is known as a "054". You can see a list of 054 batteries here.

Sizes of 054 batteries vary, so as I said above, the i-MiEV needs a battery less than 184x133x204 mm (exc. terminals). Batteries are measured at their maximum and often have a lip at the top, so you can deduct a few mm for the footprint.

I have fitted a Yuasa YBX3054 36Ah (size: 187x127x223 mm) and it was almost identical in size to the OEM and fitted fine. This battery is listed as having standard terminals, but it actually has Japanese terminals with the collars fitted to enlarge them to the UK standard.

Batteries that do look like they could fit are:

• Yuasa YBX5054 40Ah ,size: 187x127x223 mm, standard terminals. Similar battery as above but with 5 year warranty rather than 3 year.

• Duracell DA40 40Ah, size: 187x127x220 mm (height exc. terminals is 204 mm), Japanese terminals. Others on forums say they have used this battery.

• Exide EB356 36Ah, size: 187x127x220 mm, Japanese terminals.

• Bosch S4 018 40Ah, size: 187x127x227 mm, Japanese terminals.

If using a battery with Japanese terminals, you will need a set of collars to convert them to the wider size. You can source these cheap on eBay - search for "Japanese battery adapters". The Yuasa YBX3054 battery I used came with them fitted.

There may be other batteries that will fit, but after looking at most of the common brands, most others, including the Numax 34B19L (same number as the OEM battery) seem to be physically too large to fit in the i-MiEV. Some others, like the Bosch S4018 may just fit, but on paper seem too tall , but may fit if you remove the plastic tray it sits in.

If anyone has fitted anything different, please do let me know and I'll add the information here.