Member Since: 24 Sep 2013
Location: Cheshire
Posts: 198
Charging additional battery via boot 12v coonection
Hello all,
I need to do a little more investigation, but wondering if I can use the cig lighter connection circuit in the boot to charge a small leisure battery?
Ran the weaco off the 12v plug in the boot this weekend, but need to check if its a switch live with the engine running/ignition on. Just made sure to unplug it when I parked, so it would not discharge the main battery. Need to check if its a constant or switched live.
Im wondering if its a easy way to charge a small battery in the boot that would run the fridge on its own when the car is turned off.
Anyone done it that way?
I wanted to install a additional battery under the bonnet, but I have the aux. Heater and so the space for the second battery using the front runner plate is not there
12th Sep 2021 7:05 pm
DSL Keeper of the wheelie bin
Member Since: 11 May 2006
Location: Off again! :-)
Posts: 72775
Rear socket shouldn’t be live with the ignition off, unless someone’s put a jumper in place of the rely so it’s perm live.
12th Sep 2021 7:11 pm
Gareth Site Moderator
Member Since: 07 Dec 2004
Location: Bramhall
Posts: 26699
I have. A few years ago I went to LeMans 24. I was going to be camping for 4 nights, and didn’t have an aux battery in my D4. I have an Engel MT45.
I put 3 small leisure batteries across the back side of the load barrier, and secured with a ratchet strap. They were wired into parallel to give me 12v and lots of amp hours.
The batteries lasted the 4 days easily. When I got home I made a small experimental accessory socket to battery lead. I thought the worst that would happen is that the fuse would blow when I started the engine with the batteries in a relatively discharged state. However it didn’t and the voltage seen by the batteries when the engine was running was the same as the vehicle battery. So I can only presume that it was charging them up.
My only other concern would be overloading the wire if any big current items were switched on with the engine running, like heated screens or seats, but it was 30 degrees so no need!
Probably ultimately better to get a proper split charge system, but if it’s a basic need then it seems to work. My car didn’t catch fire, the fuses were fine and the beer was kept cold.
12th Sep 2021 7:15 pm
Mk1Rally
Member Since: 24 Sep 2013
Location: Cheshire
Posts: 198
Thats good to know, thanks.
Yes, the biggest concern would be the amount of current drawn from a heavily discharged leisure battery once the engine start and the crt was live. I bought a really simple split relay for a T4 van I had years ago. The gauge of the wire and the contact size would apparently restrict the amount of current you could put it..I think that was 20 or 30A..which in real terms is far more than a trickle or solar panel (of a manage size) could chuck at the battery.
Yes, a proper split charge set up is better, but in this car it would be to run the small Weaco (26ltrs) off and that would be it. I want to use one of these small form ones you can get for motorhomes, and ideally install it behind the plastic panel where the Jack/handles are fitted. Need to look at sizes
Im hoping I dont need to use it to supplement the starter battery. So would not need to join the crts.
12th Sep 2021 7:28 pm
Johnny Oxford
Member Since: 14 Dec 2014
Location: Chinnor
Posts: 515
following with interest, I have 2 really good (and expensive!) LiFePO4 leisure batteries which I no longer use for their original purpose, and am thinking of doing similar, my batteries are Tracer
Discovery Sport SE (awful)
56 plate D3 HSE TDV6 Zermatt Silver
Defender 90 200tdi
13th Sep 2021 9:15 am
Mk1Rally
Member Since: 24 Sep 2013
Location: Cheshire
Posts: 198
Thats a interesting bit of kit.
Whats the physical form size of the battery you are thinking of installing behind the panel
We do use the 7 seats occasionally, so looking to try and avoid a big electrical install in the boot space, so all i have to do is take out the dog guard and the drawers, if they are fitted. Keeping the look clean other than a Voltage display in boot
13th Sep 2021 9:34 am
Johnny Oxford
Member Since: 14 Dec 2014
Location: Chinnor
Posts: 515
165 x 125 x 110mm
They are really high end batteries, had them several years, used to run a 12 volt inverter off of them for mobile use of a large PA system at festivals.
Havent tried them in the boot space covers yet but Im pretty sure they'll fit.2014 D4 HSE Facelift Corris Grey
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Discovery Sport SE (awful)
56 plate D3 HSE TDV6 Zermatt Silver
Defender 90 200tdi
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