Paul C. Buff, Inc. Technical Forum

I have a question about a possible alternate use of your VML battery. My son is getting his second PowerWheels battery powered "vehicle" and the SLA batteries they use are notorious for living a very short life if not properly maintained (and to a degree even if they are). I was wondering if the VML battery would work for this application or not. I'm not sure what kind of current the PowerWheels draw, nor am I sure what kind of continuous current the VML battery can supply. I'm also curious as to what the effects of fully draining a VML battery would be, as I'm pretty sure I read that the VML has a shut-off in it for when the battery gets low, and I'm sure that's there for a reason. Voltage-wise, I think I'd probably be OK as I assume the 14.8V rating of the VML battery is an actual rating, and should be close enough to what a fully charged 12V SLA battery provides.

I understand you're not going to be able to make any guarantees or promises here, but if you could at least provide the specs of the battery and some insight into what happens if if is fully discharged, that would be helpful.

The VML battery is 14.8VDC, with a max continuous current of 30ADC. The cut off voltage is 11VDC. It will not drain fully.

Just an FYI.... I had been thinking about mod'ing my kids' JD Gator Power Wheels and from Google it looked like depending on the particular vehicle and rider weight that the motor usually draws well under 30 amps. Let us know how it goes :)

Thanks for the quick response. To be clear, the "cut off" is in the battery itself? I guess I had just assumed it would be in the inverter, but if it's in the battery, that's all the better.

My other question is, is it possible/safe to hook two VML batteries in parallel? It looks like the Powerwheels batteries are 12AH while the VML is only 8AH. However, my suspicion based on the information Paul has posted leads me to believe I may still get more runtime out of one of these than I would out of an SLA.

Yes, the cut off is in the battery. When using in the inverter, one can run them in parallel. The Lithium batteries run a 90%+ efficiency, vs the 65-70% from an SLA.

Cool, this is sounding promising. If you can run them in parallel in the inverter, I don't see any reason why they couldn't be used in parallel for other purposes.

Would they also be able to be charged in parallel using the VML charger, or would you need to charge them separately?

One other question - you said the max continuous current is 30A - I assume there is a higher peak rating? Do you by chance know that?

Thanks for the heads-up. I have been doing a little surfing this afternoon and am finding that what some have done is used a 24V scooter speed controller, which will coincidentally limit current draw to 30A, and then run two 12V batteries in series and use the speed controller to drop the voltage back down.

Theoretically doing this with the VML batteries would provide a much longer run time than the stock 12AH battery, and wouldn't suffer from any of the sulfating issues that SLA's have. The only question is, is it worth spending $180 on VML batteries for a ride-on toy we got on clearance for $150? :roll: I don't currently own any VML's but I guess this would be an easy way to convince my wife we need a couple.

Minor note - VML battery is 14.8V at half charge, and 16.6V with full charge. SLA batteries are 12V at half charge and 12.8V at full charge. The drop from 16.6V to 14.8 doesn't lengthen recycle as the inverter responds to battery power output rather than battery voltage.

SLAs slow down dramatically in cycle time as they discharge because internal resistance rises significantly as the charge is depleted. VML Lithium maintains constant recycle times until the end because internal resistance doesn't increase.

VML battery produces equivalent number of pops (useable Watt Hours) as about 14AH SLA battery. This is mostly because of the increasing internal resistance with discharge.

Reviving a very old thread. I finally got around to trying the VML batteries in a ride on toy. What I found is that once it is moving it works great, but it seems to struggle to provide enough current to get it started unless you start it on the low speed and them shift to high.

That said, if I took two fully charged batteries and connected them in parallel to power the vehicle, would that cause any problems with the batteries? I know you said previously that you could use two in parallel with the inverter but I'm not 100% sure if this would be any different.

You're exploring uncharted territory here, so we can't give you guaranteed accurate info.

First, to run VLM batteries in parallel, you would have to keep them at pretty much the same charge level. Placing a fully charged battery across discharged battery could cause damage to one or both batteries. I discussed parallel operation with the manufacturer and their first response was positive. But when I brought up the unequal charge possibility they urged caution.

I assume one could parallel two batteries and charge them together with a single charger. But that's only an assumption.

As for the 30A max current, that is short term peak current. In the VLM, the actual operating current is about 20A. Operating continuously at 30A would overheat them and possible cause a fire.

As for the battery's low voltage shutoff, Lithium batteries can suffer a condition not unlike sulfation if completely discharged. So the batteries contain a circuit that shuts them off internally before they reach the point where they would otherwise be damaged. However, we have recently been informed that the internal control circuitry continues to draw a small amount of current even after the batteries are shut off.

So, while they don't start being damaged immediately like SLA batteries that are fully (or even partially) discharged, VLM and similar Lithium batteries will eventually become useless if left for long periods of time in the discharged state. How long? I really don't have accurate info here, but I suspect several weeks. (SLAs begin to sulfate immediately, even mildly at 1/2 discharge, and can become useless within a day or two if stored completely discharged.

Finally, I should say that essentially all Lithium batteries for "e Bikes" are the LiFePO4 type used in our new VLX™ rather than the NMC type used in VML™ and laptops, cell phones, etc.

An excellent discussion of all Lithium battery types can be found here:

http://batteryuniversity.com/learn/arti ... ithium_ion