Hi, anyone know where the auxiliary battery is located on 2005 alphard hybrid campervan, problem is the car won't start without a jump start there is a battery below the gear shift but i think this is a leisure battery. thanks.

Mine is under the driver's seat

I have also found I can jump start it with my noco attached to the leisure battery, which is a boon when it's raining

Edited May 2May 2 by Sunny
Forgot to add some info

Yes, leisure batt under gearshift & aux 12V under drivers seat in my conversion. There is also a shrouded positive terminal under the bonnet for jump starting i think.

Who did your conversion?

Don't know who did the conversion, but the info about the drivers seat, is what I was looking for, I had read somewhere else it was under the passenger seat but mines has a heater unit fitted there.. hoping it's just the auxiliary battery that's dead, or could be looking at major expense for the DC to DC converter.

Thanks for your help.

Under the passenger seat on a hybrid is the battery cooling fan, relays, battery ECU and one end of the hybrid battery assy. The aux 12v battery on mine is under the drivers seat the original fitted by CampervanCo was a Optima Red Top Starting only 44Ah 730A which was a mystery to me because the Hybrid does not need a high Ampage battery as the hybrid battery starts the engine, but it does need a high capacity. I managed to squeeze in a slightly larger battery Exide AGM 62Ah, 680A part number EK620. L02 size 242 x 175 x 190. There is quite a high drain on the battery when parked up for any length of time from various ecu's alarm radio central locking, and once the battery has been discharged it won't be able to supply enough power for the hybrid ecu to start the engine. on turning on the ignition I have found the voltage can drop by nearly 2 v.

On the 2005 hybrid Alphard conversions Iv'e seen, the aux 12V is normally under the drivers seat, and the passenger seat area is taken up with hybrid bits (cooling fan, relays, battery ECU and the end of the traction battery). So if you have a heater unit under the passenger seat, that does not rule anything out. It is very likely the 12V is still under the drivers seat or has been relocated nearby by the converter.

A flat or weak 12V battery will absolutely stop a hybrid from booting up properly even though the traction battery cranks the engine. The car still needs a stable 12V supply to wake up all the ECUs, close the HV contactors, run relays, etc. It is common to see the voltage look OK at rest then drop hard when you go IG ON, and if it dips too far you get no READY and lots of odd symptoms that look scarier than they are.

A few practical checks before worrying about the DC DC converter. First one would be to measure the 12V at the battery posts with a multimeter: engine off should be roughly 12.6V fully charged, 12.2V is already pretty low.

or Watch it while you go to IG ON and then try for READY. If it drops into the 10s, the battery is suspect even if it is “newish”.

or once you do get READY, the DC DC converter should charge at about 13.8 to 14.4V at the 12V battery. If it is still sitting at 12.x when READY, then you start looking at DC DC, fuses, wiring, earths. If it does need a battery, capacity matters more than silly high cranking amps on these. AGM tends to cope better with the constant parasitic drain from alarms, ECUs, locking, etc, especially if the van sits. Also worth checking for any additional leisure battery split charge setup the converter fitted, as a wiring fault there can flatten the aux battery quickly.

If you can post what symptoms you are getting (no READY, dash lights, clicking relays, etc) and the voltages you measure, people can usually point you the right way pretty quickly. Let us know how you get on.

Good luck mate!