Dead 12v Battery --- A Glove Box Remedy?

I bought one of the BB7B's when I saw it on the shelf at Target. I'm not sure if this has been mentioned, but the real appeal of this thing for me is the small size. It fits in the hidden trunk compartment on the side opposite the battery.

I had the opportunity to test it out on a dead prius battery last night. Unfortunately I haven't yet gotten around to wiring an always on power port, and my Prius didn't have enough power to engage the power ports, so it had no connection and hence was useless. I ended up calling roadside assistance.

So know that you WILL need to rewire an always-on power port if you want to rely on the BB7B.

 

I am actually planning on installing an unswitched 12V power port connected directly to the 12V prius battery (through a fuse of course). I'd like to have convenient access so I could plug in a 300W inverter to drive appliances when I'm on the road. Once that is installed, I'll be able to just plug the BB7B into that whenever needed.

But upon seeing this thread, I ordered the coastal kit. Even though the front power port doesn't have the juice to run a 300W inverter,having it always on would be useful for the exact thing you are doing: Keeping the BB7B topped up by plugging it in frequently.

 

I just had the opportunity to test out my BB7B under controlled conditions on my 2004 Prius. It worked well.

Here's how I drained the battery for testing:

My Prius 12V battery is on its last legs, and I was able to drain it down by leaving the headlights turned on for about a half hour. It was actually kind of interesting watching the car slowly die. After about 20 minutes only one of the two headlights would run. Then even that one wouldn't run. I kept discharging the battery by connecting a 300W indoor halogen light directly to the battery while monitoring the battery voltage, which was now below 10V under load. It burned very dimly, probably not using more than 30 or so watts, and I only ran it approx 5 minutes after the headlights died. Soon the door ajar beep beep beep turned into a long kind of pathetic drone, and then I decided I had probably got it low enough.

I tried starting the car, and it wouldn't start (first time in my life I was thankful for that! :evil. Annoyingly the car also didn't seem to have enough power to turn itself off; pressing the power button cycled between the green light and amber light modes, but wouldn't turn the power button light off (I've seen this in the past on dead batteries so it's not a big surprise). And reassuringly the car did turn off at one point although I wasn't sure how I made that happen.

The results:

The battery was reading about 7.1V under load, but when I disconnected the load it started heading back up resting somewhere just below 10V.

I hooked up the BB7B to the front 15A outlet that I had rewired to be always on, and switched the BB7B into boost mode.

The car didn't start up when I tried it immediately, or after a minute of boosting. But after a few minutes of boosting it did start up.

Annoyingly, the multifunction screen continued to say the transmission is abnormal and needed to be returned to park, even though it was already in park. I got around that by shifting to neutral, which removed the full screen warning, but the MFD still said simply "Problem" and the dashboard big red triangle with exclamation symbol remained lit. After running the car for about 5 minutes I powered it off and then powered back up without the BB7B.

The "Problem" message on the top of the screen and the light remained lit. I drove the car around the parking lot, and again powered it off then on. This time the Problem message and light were gone and they never came back.

I've seen that behavior before where the transmission Problem screen comes up; it seems to happen every time I jump a dead battery in my Prius. It's nice to be able to explore it under controlled condtions and realize that it seems to always go away eventually, and the car is still driveable even when the Problem light is on. Someone on this forum said the transmission Problem screen is a red herring, that it comes on because the computers are clueless due to having lost power. I'm now thinking this is true, that it is a red herring and not something to worry over.

Anyway, I'm now feeling happily confident about the BB7B. If it can take a battery from 7-10V back into operation, that's a pretty good sign.

I'm going to replace my Prius 12V battery soon, but if there are any more quick tests I should do on the last legs battery, please let me know.

 

Fascinating. Since you have the ability to measure battery voltage, it may be interesting to measure how much voltage the BB7B produces in boost mode. If much more than 13.8V, then you may not want to have the Prius electronics in the loop while the boost is in effect.

I also suggest that after allowing the 12V battery to discharge so deeply, that the battery will need to be charged up fully (one way is by leaving the car READY for an hour or so).

Good luck with your new device.

 

my battery hasn't held a charge since i reached 43k miles or so. i let it drain too many times so the charge only last 16 hour or so... so if i sleep in, or don't drive for a day, it's dead... 9v or so

the car starts fine when supplied with over 10v.. under and you'll get the various warnings about the parking pin.. if you let the car sit and charge up a bit... then power off and on... you can hit the park button a couple times and it shuts up...

i've attached 4 7v solar panels in two 13.5v series (a few panels read lower, so i arranged them to obtain the similar voltage readings) i can leave the car all day, and it's just enough to keep the battery up. right now my install is temp, so i have a long wires that go from my dash to the battery. i'm thinking of moving them to the roof...

 

My OEM 12v battery was also on it's way out and just before I replaced it I was able to run it down by simply having the doors open for about an hour while detailing the car. The transmission parking pawl solenoid seems to drop out at around 10v giving you random assorted errors.

My solution: Optima yellow top battery:
http://www.amazon.com/dp/product/B00075OSD8?tag=priuschatcom-20
:bounce:

I recently forgot to turn off a map light for about 2 hours and it didn't even register a significant drop in battery voltage. This would have killed my old battery.

 

Indeed, I have to give Sparky a shout out too. While I was doing the battery draining experiment I was taking apart my dashboard with Sparky's guide, to work on the radio. Thanks Sparky for your contributions that help us all.

I saw that it is definitely way below 13.8V while the BB7B is boosting a drained battery; the battery sucks up all the current. I wouldn't worry about damage as long as you remove the BB7B soon after the car has started. The BB7B does make a whining noise while boosting, which indicates to me that it's using some sort of a switching dc/dc voltage step up system to output more voltage than the BB7B internal batteries put out. If so, then it likely has voltage regulation.