Adding a second battery on the rear rack

Hikertrash

Member
Using one at a time, I'm adding a second battery in parallel on the rack. The stock battery when turned off shows no volts, however the new UPP rack battery shows 25 volts in the off position. Both batteries, measured separately, show about 54.6 volts with full charge in the on position. I had intended to put both keys on one ring so only one could be used at a time, but since the second battery shows 25 volts I'm reluctant to do this, and for now plan on unplugging the second battery when using the stock battery.

Am I in danger of frying the motor with the second battery showing 25 volts in the off position and the stock battery turned on?
 
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Hikertrash

Member
Using one at a time, I'm adding a second battery in parallel on the rack. The stock battery when turned off shows no volts, however the new UPP rack battery shows 25 volts in the off position. Both batteries, measured separately, show about 54.6 volts with full charge in the on position. I had intended to put both keys on one ring so only one could be used at a time, but since the second battery shows 25 volts I'm reluctant to do this, and for now plan on unplugging the second battery when using the stock battery.

Am I in danger of frying the motor with the second battery showing 25 volts in the off position and the stock battery turned on?

Weird, even though a Fluke meter shows 25 volts in the off position, the battery won't light a cheap test light. It does light in the on position. I guess I won't worry as long as at least the batteries (stock or rack) is in the off position.
 

harryS

Well-Known Member
That 25 volts is leakage in the battery BMS. Not that unusual. If connected to a load, like your test lamp, and it discharges, that's OK. Your controller, even if turned off, would discharge it too. If the lamp stayed on, the BMS is defective,

Just the same, I would prefer it when there is no leakage. I've never seen it on my UPP batteries.
 

Hikertrash

Member
That 25 volts is leakage in the battery BMS. Not that unusual. If connected to a load, like your test lamp, and it discharges, that's OK. Your controller, even if turned off, would discharge it too. If the lamp stayed on, the BMS is defective,

Just the same, I would prefer it when there is no leakage. I've never seen it on my UPP batteries.

Thanks for the explanation.

I have another question. I also have a 14ah battery for the XP from Aliexpress. It shows 37 volts in the off position out of the bike on the meter. The test light doesn't light (EDIT: is barely lit). When in the bike, in the off position, if I try to turn on the bike, the display will flash briefly once. Do you think it will be OK to have both off-brand batteries attached to the bike as long as one is in the off position?
 
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harryS

Well-Known Member
If you could arrange to do so, and it's probably not easy because one battery is in the frame, just connect one battery at a time. Nothing goes wrong that way, You probably have to stop and turn the rear one on anyway.

With both batteries connected all the time, you have to make sure you don't have one at full charge and the other at discharge, and both of them turned on. It would probably be better if you connected the packs at full charge, and left both on, Working together, they work less hard, and that improves life. DIsconnect to recharge.
 

Hikertrash

Member
If you could arrange to do so, and it's probably not easy because one battery is in the frame, just connect one battery at a time. Nothing goes wrong that way, You probably have to stop and turn the rear one on anyway.

With both batteries connected all the time, you have to make sure you don't have one at full charge and the other at discharge, and both of them turned on. It would probably be better if you connected the packs at full charge, and left both on, Working together, they work less hard, and that improves life. DIsconnect to recharge.
My intention was to have the two keys on one ring so I'd be only using one battery at a time. I'm a little concerned with one on and one off, that leakage from either off-brand battery can mess up the other, the controller, or the motor.