Batteries wired in parallel are now fully charged

Dead Power Wheels Battery? Maybe You Can Trick it Back to Life! 1

It’s a story that repeats itself in garages across America every summer. Your kid wants to drive his Power Wheels Jeep, or her Power Wheels Escalade (is it really selling for $800-$900 on Amazon?)… and the battery is dead. You plug in the proprietary charging connector (if you haven’t lost it, that is), but the battery is too dead to charge. And even if you could rig up some sort of method to connect it to a “smart” 12V battery charger like the CTEK models I’ve reviewed in the past, the battery is too dead for the smart charger to sense it, so you end up with an “error” light. Which means you’re about to spend $56 for a new Power Wheels battery so your daughter can terrorize the neighborhood in her pink Barbie Cadillac Escalade:

Pink Power Wheels Cadillac Escalade

Pink Power Wheels Cadillac Escalade

Not so fast…

Remember this scene from Princess Bride? “There’s a big difference between mostly dead, and all dead.”

It’s possible that your Power Wheels battery is only mostly dead, which means there’s a chance you could revive it with this trick.

Forget the cheap-o OEM Power Wheels wall-plug charger. I took a pair of wire cutters to ours long ago. It’s a “trickle” charger, not a “float” charger, meaning it delivers a constant trickle of 12 volts at a low amperage to slowly charge the battery. But because the charger has no circuitry to measure the charge level of the battery, it never stops charging… which is why the manufacturer warns you not to charge it for more than 24 hours at a time. But nobody remembers to do that, so we all end up with over-charged (dead) batteries, or batteries that we forget to charge at all… which also end up dead.

A “float” (or “smart”) charger also delivers a low-amperage charge to the battery, but features circuitry that senses when the battery is fully charged. When that happens, it stops charging and only monitors the voltage. When the batteries voltage drops enough, the charger re-activates and fills it up again.

Like I mentioned above, I’d snipped off the “wall wart” adapter portion of our Power Wheels charger long ago and crimped a female spade connector to each lead, giving me something metal to which I could attach charging clamps from my trusty CTEK 7002 smart charger, which kept the 12V Power Wheels battery at the ready without risk of over-charging. But I use my charger for other stuff, too… meaning I sometimes let the Power Wheels battery sit for months without charging. So when I went to try and charge it yesterday, my smart charger sensed too little voltage to even register the existence of a battery on the other end, so the charger lit up its red “ERROR!” light.

That’s the main drawback of “smart” chargers… sometimes they’re too smart for their own good. But because I had those female spade connectors crimped onto my Power Wheels charging plug, I was able to “piggy-back” charge it by wiring it in parallel with a separate 12V battery, like this:

"Piggy-back" charging a mostly-dead Power Wheels 12V battery with another 12V battery wired in parallel

“Piggy-back” charging a mostly-dead Power Wheels 12V battery with another 12V battery wired in parallel

Prior to hooking everything up, I made sure the black 12V Werker battery shown above was fully charged to the point that that my charger lit its green “full” LED.

Then I connected everything as shown in the above photo: the positive spade connector from the Power Wheels plug is connected to the positive terminal of the fully-charged 12V battery, and the negative spade connector is on the full battery’s negative terminal. The “thirsty” Power Wheels battery immediately began drawing a small amount of charge from the fully charged battery, so that the combined voltage of the two batteries was well below 12V on my multi-meter. When I attached my charger clamps to the battery terminals (positive to positive, negative to negative), the charger sensed the circuit’s voltage, and decided it was was low enough to require charging, so it started charging. You can see in the first photo that the charger’s status LED is showing “more than 50% charged.” After a few hours in that state, the light turned green:

Batteries wired in parallel are now fully charged

Batteries wired in parallel are now fully charged

At this point, I disconnected the black 12V battery from the circuit completely, and connected the charger to only the leads on the Power Wheels charging plug:

Previously, the Power Wheels battery had been so dead that the CTEK charger gave up and turned on the error light. But after being wired in parallel and “piggy-back” charged, the Power Wheels battery had recovered enough to allow the smart charger to “see” it and start charging, so I let it charge like this for another hour or so before I checked it again. Eventually, the green LED indicated that the Power Wheels battery was fully charged. I disconnected the charger and confirmed with my multi-meter: a victorious 13.2 volts!

I put the battery back in the pink Escalade, and it ran like a champ. Because of its age, it’s hard to say whether this battery will still provide runtimes as long as it did when it was new. It probably won’t. But the good news is that it’s not all dead, and it’s not even mostly dead any more. I’ve dodged the $56 new Power Wheels battery bullet for at least another day. 🙂

Keep in mind this trick only works with batteries and chargers that use the same voltage — 12V in this case. If you have a 6V Power Wheels battery, you’ll need a 6V charger and another 6V battery to piggy-back. Do NOT try to charge a 6V battery with a 12V charger or “host” battery. Also remember that when you wire two batteries together, it really makes a huge difference whether you wire them in parallel, or in series. If you don’t know the difference or why it’s important, do some web searching on batteries in series vs. parallel before you start tinkering.