Apologies for the delay
@Jallu.
You are correct. The 48v battery (in terms of watt hours) is greater than the 52v. However please understand that by increasing the voltage of a battery pack, you are increasing the power flow. Thus, increasing the efficiency as the amps don't need to be as high to compensate for discharge.
I'm still calculating whether the range is better with either the 52v15amp vs 48v17.5amp. The performance is better due to the efficiency.
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But I'll be playing around with gear ratio courtesy of the Christini Spider adapter, which allows the use of a 32t chainring.
I'll share my findings if it assists others. But
@Mabman has been using both the E22 with both a 52v battery and the Christini spider adapter.
As for building a battery. Yes, it is possible. However, this particular frame/battery design uses a switch which activates the BMS within the battery.
The above video should elaborate on this further.
If you consider building your own battery, I would reccomend removing the battery mounting hardware and fabricating something which would work with a DIY battery and use Anderson connectors