It looks like a standard Hailong case to me. They're all over Ebay, Amazon and Aliexpress as well as available from all our favourite suppliers. You need to take your battery off and take some decent photos of it because there are some minor differences in the various types.
12.5 and 7.5 are the number of amp-hours in each one, which is the capacity. You can get a battery with whatever capacity you want. Generally, the more amp-hours, the heavier the battery. The more capacity, the further you can go and you get slightly more power.
The specific Eleglide battery will most likely be a lot more expensive than an identical unbranded one.
This is probably it (select 4-pin version), but you must show photos to be sure:
1.Technical Data Item Specification Battery Model EBBK-036130-HL1 Voltage 36V Capacity 13Ah Cell High Power Li-ion LiNiCoMnO2 Weight(with holder) Appr. Energy 481Wh Cycle life(time) 500 Times ≥70% Capacity Discharge Standard Current 10A Max. Current(Continuous) 20A Protect Current 50A End...
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