OK, a couple of years ago I mounted my Nexus 7 tablet in the dash of my truck. It worked great, added a usb-hub, an amplifier, a software-defined-radio, a can-bus receiver for steering wheel controls, a backup camera plus usb composite decoder. All was good. At the time I had this internal mental battle about how to charge it. I ultimately removed the internal battery and just ran it straight of a buck-converter. I also had this internal mental battle about using the 'Retained Accessory Power (RAP)'. This (documented in the GM upfitters guide) gives you power to accessories until about 30s after you open a door. However, the tablet is slow to boot. So my thinking was, when I turn off the key, have the tablet go to sleep. It only draws about 2mA when sleeping (just refreshing dram), and that is about the leakage current of a big lead-acid battery anyway, so how could this matter?
Fast forward a few years. It mattered!
So some wretched app updated itself and did the usual 'hot-pocket' thing we all know from our phone. Went beserk and prevented sleeping. So I get home yesterday, the truck in the garage so the hood is right tight to the front and corner, w/ a shelf on the other side. I turned it off. It hooked to the garage WiFi, upgraded something, and, well, never went to sleep.
So I get up this am, and i have an 11am meeting (yes us unemployed people have meetings!). I go out about 1030 am and.... nothing.
Now, my truck. Its this weird combination of high and low tech. Solid live axle, drum brake, leaf springs? check. But, tt has a cool feature, a low-voltage cutoff. If the battery hits 9V, some high-power actuator moves a bar, and cuts it off. So this is what has happened, we have drained to 9V, and hit the cutoff.
Sigh. Now what, i mean, its wedged into the corner, can't get @ the hood.
OK, lets drop it into neutral and give it a shove right? Wrong, need hydraulic pressure to release the parking pawl. Hmmm.
OK, its a true 4-wheel drive, so i can put it into dolly-towing mode by disconnecting both transfer cases right? Argh, that is an electric function. OK, think. We are not going to let this beat me. So, if i was to take 3 x 18650 battery, and some not-too-thick wire, and jam them into the cigarette lighter, that would put ~12V there, but the thinnish wire won't pass more than the 20A the fuse is rated for (those 18650 can pump serious current otherwise). OK, do that, now we have accessory power. No, we are not going to crank the starter, that would be crazy. But, we can indeed move the 4WD switch, and, we can drop it into neutral front-to-back and neutral front. Now, we can give it a shove (its heavy!), and, get in there w/ the quick-charger. And boom, we are started.
Well, that was easy.
I have made the assumption that the hard-reset of the tablet resolved whatever miscreant app was there, so no point in ever checking that again, i mean, how could this re-occur? Look for updates later 🙂