# What are safe voltage differences to connect 2 batteries in parallel? [closed]

I have a OneWheel electric skateboard with a 58V LiFePO4 battery 130Wh (I believe 14s1p configuration).

There is a method in practice where owners wire EGO LION battery packs (56v 2.5Ah=14s1p, 5Ah=14s2p, 7.5Ah=14s3p) in parallel to their OneWheel onboard battery. Due to their internal parallel configurations, I believe the EGO batteries can flow AMPS as follows: 2.5Ah=20A, 5Ah=40A, 7.5Ah=60A.

I have measured the AMP flow @ 5.5A spike then ramp down to 3A within about 30 seconds when connecting a full 5.0AH EGO to a 85% charged OneWheel (voltage differences of roughly 58V connecting to 54V).

I do not know the internal resistance of the onewheel battery other than my observation above.

My questions are, what is a practical safe voltage difference to connect a full EGO battery to a slightly discharged Onewheel for use in the real world?

Is there a way to graph initial expected amperage currents given onboard battery voltages of the onewheel? (58v=100% - 48v=0%)

• What do you mean by "safe"? – Bob D Feb 4 at 16:15
• I guess I'd quantify "safe" as low enough current that damage to the onboard pack would not be expected in practice. I realize the technically correct answer is exactly equal voltages. – deanhuff Feb 4 at 16:30
• But if you don't know what that current level is, how can you expect an answer to the title of your post? – Bob D Feb 4 at 16:33
• If you re-ask this question somewhere else, you should say whether you are asking about the safety of using batteries with different nominal voltages in parallel, or about safe methods of equalizing the voltage of batteries before you (semi)permanently connect them. – Solomon Slow Feb 4 at 18:08