Backup Car/truck Battery

Mentioned in another thread I like doing some electric/electronic tinkering. I'm no EE degree holder and my projects and hacks are pretty tame as far as that goes, but like to believe I can think outside the box for repurposing some off-the-shelf items and hack them to fit my needs. And as much as I hate to admit it, the Chinese electronic items and modular assemblies on amazon and ebay are dirt cheap and fun to play around with.

So my last electronic preparedness related project was with to a vehicle jump starter I got free from work. It's a small lead acid battery meant to carry in your vehicle to jumpstart it in case the primary battery dies, but it also has a powerpoint/cigar lighter and USB charging sockets for powering or charging items like phones, radios, air compressors, etc, that might be helpful to have in a bugout too. Problem was, it requires at least monthly recharging and the only unattended and safe way to do that (per the manual) was using 120 volt AC house power. Well, Murphy's Law pretty much guarantees that if I ever needed to use it, it'd be a 2 or more months after I forgot to recharge it. Stupid design, IMO, since all vehicles have an alternator for charging batteries but this unit requires me to remove it from the truck and plug it into house power every month?

So I'd looked into this before, and the answer for charging a spare battery in a vehicle is with a battery isolator that are commonly used in RVs and campers. It isolates a spare battery so the alternator will charge it, but stops any reverse current flow so the vehicle can't draw power from it. Else, you might just end up with two dead batteries which defeats the purpose obviously. The battery isolators aren't cheap, the installation can be tricky, and at least in my truck there's no room under the hood to even hold a second battery. They're also designed to put out high amperage to charge the spare battery faster, but that means they require heavy gauge wire - and for longer the wire runs (like from the alternator in the engine compartment to the bed of a pickup truck which is the only place a spare battery will fit in mine) means even larger gauge wire which isn't cheap either.

Enter the $13 CCC (cheap Chinese crap) solution. https://www.amazon.com/Controller-Waterproof-Y-SOLAR-Lead-acid-Discharging/dp/B00XTQ76WW

It's a PWM charge controller meant for small solar power setups. It's designed to take the 13-18 (roughly) volts output from a solar panel and charge a 12 volt battery smartly so the battery isn't damaged from overcharging. But 13-18 volts DC is 13-18 volts DC, the controller and the battery doesn't know or care whether the voltage is coming from a vehicle alternator or a solar panel.

Now I wouldn't recommend wiring this to any vehicle safety related wiring, but my truck has separate wiring to power a third brake light and dome light so I tapped off that for connecting to the "solar power" connection on the charge controller since if there were to be a failure it doesn't affect anything critical to the operation of the truck. Tapping power from the trailer wiring harness might be an option too, I just used the dome light wiring because it ran right next to a good spot to store the jump starter.

The "battery" side of the charge controller is connected through a single pole single throw switch so I can turn off the battery charging if desired, and then wired to a cigarette lighter plug (taken from the electronic junk drawer) and plugged into the jump starter socket. I've had this installed for a couple months now and finding that if I drive the truck more than about 30 minutes each day that the jump start battery stays at full charge all the time. The charge controller only charges the jump starter battery when the voltage rises above 13 volts, so it won't drain your starting battery to charge the jump starter.

Hope someone finds this useful, or can suggest even better/cheaper modifications. There's nothing that requires that it be a jump starter like the one I have either, connecting a regular car battery (or deep cycle one) works too. Just replace your current battery while it's still good and keep the old one as a spare. Two batteries is one battery, and one battery is none right?

 

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There isn't a reverse current / discharge problem, or not other than the normal discharge of a sitting battery loosing it's charge over time. The charge controller has built-in protection so the jumpstarter battery doesn't discharge back through the truck wiring.

I did have to add a diode to the dashboard solar panel I use to keep the truck battery trickle charged. Another small truck power project from a couple years ago. This solar panel didn't have any reverse current protection and it would allow the battery to discharge through the panel after dark.



That fixed that problem.

Using that solar panel to charge the truck battery actually required another small hack as well, the cigarette lighter sockets in the newer Ford trucks (and likely others) won't allow charging the battery through them. They must have some reverse current flow 'protection' of their own that prevents it. What I did to get around that was to add a new cigarette lighter socket to the wiring for the ham radio, since I wired that straight to the battery bypassing all the truck electronics and fuse panels.



Wiring pulled out a little to see it better, but I just spliced into the radio power wiring and added the new socket.

 

To Keep my Landcruiser charged as it stands in the garage for some time ( I am retired ) , I have fitted a plug in the Radiator grill so that I plug in a automatic charger to keep the battery fully charged , I have fitted a bright LED on the ingoing charge cable so that I see it is plugged into remove before driving out of my garage ,Also an inline fuse for safety, My cruiser has 2 batteries in the engine compartment , both are kept charged you could do something similar , as it is a back up you would not need to have it going through the vehicle system , only connect to the vehicle if / when it is needed , just an idea

 

Good idea, I wish I had space to install a 2nd battery in the engine compartment. This project was mainly to make a free battery I received more user-friendly by automating the charging process. Couldn't agree more that having one isolated from discharging through the vehicle normally is critical for redundancy.