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razor scooter converted to automotive relay

I rewired my kids e175 and a e100 razor scooters to run on an automotive relay. It runs great using the factory throttle. I used an On-Off-On toggle switch to isolate the charger circuit so the hot lead from the charger is not competing with that rest of the system. all of it uses a common ground though. The batteries are wired in series.

Everything works except the charger seems to not shut off when the batteries reach full charge. 

I've melted down/exploded one set already and came close to a second of batteries last night. everything I've read says that the float control is in the charger but maybe it isn't. Do I need to isolate the ground circuit? 

Although we do not recommend using a common ground (grounded frame) because the parts on the scooter are not designed for it, we do not feel like it would be the cause of an overcharge problem. 

The overcharging problem could be caused by a malfunctioning charger, or by the batteries being wired in parallel instead of in series.  

Can you confirm that the float function is in the charger and not the scooter?

Maybe when I get home I can upload some pictures and you guys could help me figure it out. People keep giving them to me to fix. I think I have 5 now.

The float charge function is 100% inside of the battery charger and is not in the scooter's controller or other electronics.

We would be glad to look at your photos and see if we can notice anything that might be causing the problem. 

Here are the pics

The battery pack is 24 Volts and the charger is for 36 Volt battery packs so it is overcharging the 24 Volt battery pack and causing it to overheat and swell. 

In the photo above the battery charger specifications state that it has a DC output of 44V 1.8A and applicable batteries are 36V 12Ah. 

It looks like the scooter will need a new 24 Volt charger and a new battery pack to get it running. 

You are a genius. I can't believe I didn't catch that. I fried 4 more batteries last night in 2 other scooters using the same stupid chargers.Thank you so much for expending brain cells for me.

The scooter works. Thank you again. The kids like mine better because they don't have to kick it started (lazy little punks). 

My wiring confidence has been restored.

Thanks for the good news. It is great to hear that the scooter is now working.

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